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<!ENTITY % entities PUBLIC "-//FreeBSD//ENTITIES DocBook FreeBSD Entity Set//EN" "../../share/sgml/entities.ent">
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<article lang='en'>
<articleinfo>
<title>Storage Devices</title>
<authorgroup>
<author>
<firstname>Wilko</firstname>
<surname>Bulte</surname>
<affiliation>
<address><email>wilko@FreeBSD.org</email></address>
</affiliation>
</author>
</authorgroup>
<legalnotice id="trademarks" role="trademarks">
&tm-attrib.freebsd;
&tm-attrib.general;
</legalnotice>
<pubdate>$FreeBSD$</pubdate>
<releaseinfo>$FreeBSD$</releaseinfo>
<abstract>
<para>This article talks about storage devices with FreeBSD.</para>
</abstract>
</articleinfo>
<sect1 id="esdi">
<title>Using ESDI hard disks</title>
<para><emphasis>Copyright © 1995, &a.wilko;. 24 September
1995.</emphasis></para>
<para>ESDI is an acronym that means Enhanced Small Device
Interface. It is loosely based on the good old ST506/412
interface originally devised by Seagate Technology, the makers
of the first affordable 5.25" Winchester disk.</para>
<para>The acronym says Enhanced, and rightly so. In the first
place the speed of the interface is higher, 10 or 15
Mbits/second instead of the 5 Mbits/second of ST412 interfaced
drives. Secondly some higher level commands are added, making
the ESDI interface somewhat <quote>smarter</quote> to the operating system
driver writers. It is by no means as smart as SCSI by the way.
ESDI is standardized by ANSI.</para>
<para>Capacities of the drives are boosted by putting more sectors
on each track. Typical is 35 sectors per track, high capacity
drives I have seen were up to 54 sectors/track.</para>
<para>Although ESDI has been largely obsoleted by IDE and SCSI
interfaces, the availability of free or cheap surplus drives
makes them ideal for low (or now) budget systems.</para>
<sect2>
<title>Concepts of ESDI</title>
<sect3>
<title>Physical connections</title>
<para>The ESDI interface uses two cables connected to each drive.
One cable is a 34 pin flat cable edge connector that carries the
command and status signals from the controller to the drive and
vice-versa. The command cable is daisy chained between all the
drives. So, it forms a bus onto which all drives are
connected.</para>
<para>The second cable is a 20 pin flat cable edge connector that
carries the data to and from the drive. This cable is radially
connected, so each drive has its own direct connection to the
controller.</para>
<para>To the best of my knowledge PC ESDI controllers are limited to
using a maximum of 2 drives per controller. This is compatibility
feature(?) left over from the WD1003 standard that reserves only a
single bit for device addressing.</para>
</sect3>
<sect3>
<title>Device addressing</title>
<para>On each command cable a maximum of 7 devices and 1 controller
can be present. To enable the controller to uniquely identify
which drive it addresses, each ESDI device is equipped with
jumpers or switches to select the devices address.</para>
<para>On PC type controllers the first drive is set to address 0,
the second disk to address 1. <emphasis>Always make
sure</emphasis> you set each disk to an unique address! So, on a
PC with its two drives/controller maximum the first drive is drive
0, the second is drive 1.</para>
</sect3>
<sect3>
<title>Termination</title>
<para>The daisy chained command cable (the 34 pin cable remember?)
needs to be terminated at the last drive on the chain. For this
purpose ESDI drives come with a termination resistor network that
can be removed or disabled by a jumper when it is not used.</para>
<para>So, one and <emphasis>only</emphasis> one drive, the one at
the farthest end of the command cable has its terminator
installed/enabled. The controller automatically terminates the
other end of the cable. Please note that this implies that the
controller must be at one end of the cable and
<emphasis>not</emphasis> in the middle.</para>
</sect3>
</sect2>
<sect2>
<title>Using ESDI disks with FreeBSD</title>
<para>Why is ESDI such a pain to get working in the first
place?</para>
<para>People who tried ESDI disks with FreeBSD are known to have
developed a profound sense of frustration. A combination of factors
works against you to produce effects that are hard to understand
when you have never seen them before.</para>
<para>This has also led to the popular legend ESDI and FreeBSD is a
plain NO-GO. The following sections try to list all the pitfalls
and solutions.</para>
<sect3>
<title>ESDI speed variants</title>
<para>As briefly mentioned before, ESDI comes in two speed flavors.
The older drives and controllers use a 10 Mbits/second data
transfer rate. Newer stuff uses 15 Mbits/second.</para>
<para>It is not hard to imagine that 15 Mbits/second drive cause
problems on controllers laid out for 10 Mbits/second. As always,
consult your controller <emphasis>and</emphasis> drive
documentation to see if things match.</para>
</sect3>
<sect3>
<title>Stay on track</title>
<para>Mainstream ESDI drives use 34 to 36 sectors per track. Most
(older) controllers cannot handle more than this number of
sectors. Newer, higher capacity, drives use higher numbers of
sectors per track. For instance, I own a 670 MB drive that has 54
sectors per track.</para>
<para>In my case, the controller could not handle this number of
sectors. It proved to work well except that it only used 35
sectors on each track. This meant losing a lot of disk
space.</para>
<para>Once again, check the documentation of your hardware for more
info. Going out-of-spec like in the example might or might not
work. Give it a try or get another more capable
controller.</para>
</sect3>
<sect3>
<title>Hard or soft sectoring</title>
<para>Most ESDI drives allow hard or soft sectoring to be selected
using a jumper. Hard sectoring means that the drive will produce
a sector pulse on the start of each new sector. The controller
uses this pulse to tell when it should start to write or
read.</para>
<para>Hard sectoring allows a selection of sector size (normally
256, 512 or 1024 bytes per formatted sector). FreeBSD uses 512
byte sectors. The number of sectors per track also varies while
still using the same number of bytes per formatted sector. The
number of <emphasis>unformatted</emphasis> bytes per sector
varies, dependent on your controller it needs more or less
overhead bytes to work correctly. Pushing more sectors on a
track of course gives you more usable space, but might give
problems if your controller needs more bytes than the drive
offers.</para>
<para>In case of soft sectoring, the controller itself determines
where to start/stop reading or writing. For ESDI hard sectoring
is the default (at least on everything I came across). I never
felt the urge to try soft sectoring.</para>
<para>In general, experiment with sector settings before you install
FreeBSD because you need to re-run the low-level format after each
change.</para>
</sect3>
<sect3>
<title>Low level formatting</title>
<para>ESDI drives need to be low level formatted before they are
usable. A reformat is needed whenever you figgle with the number
of sectors/track jumpers or the physical orientation of the drive
(horizontal, vertical). So, first think, then format. The format
time must not be underestimated, for big disks it can take
hours.</para>
<para>After a low level format, a surface scan is done to find and
flag bad sectors. Most disks have a manufacturer bad block list
listed on a piece of paper or adhesive sticker. In addition, on
most disks the list is also written onto the disk. Please use the
manufacturer's list. It is much easier to remap a defect now than
after FreeBSD is installed.</para>
<para>Stay away from low-level formatters that mark all sectors of a
track as bad as soon as they find one bad sector. Not only does
this waste space, it also and more importantly causes you grief
with bad144 (see the section on bad144).</para>
</sect3>
<sect3>
<title>Translations</title>
<para>Translations, although not exclusively a ESDI-only problem,
might give you real trouble. Translations come in multiple
flavors. Most of them have in common that they attempt to work
around the limitations posed upon disk geometries by the original
IBM PC/AT design (thanks IBM!).</para>
<para>First of all there is the (in)famous 1024 cylinder limit. For
a system to be able to boot, the stuff (whatever operating system)
must be in the first 1024 cylinders of a disk. Only 10 bits are
available to encode the cylinder number. For the number of
sectors the limit is 64 (0-63). When you combine the 1024
cylinder limit with the 16 head limit (also a design feature) you
max out at fairly limited disk sizes.</para>
<para>To work around this problem, the manufacturers of ESDI PC
controllers added a BIOS prom extension on their boards. This
BIOS extension handles disk I/O for booting (and for some
operating systems <emphasis>all</emphasis> disk I/O) by using
translation. For instance, a big drive might be presented to the
system as having 32 heads and 64 sectors/track. The result is
that the number of cylinders is reduced to something below 1024
and is therefore usable by the system without problems. It is
noteworthy to know that FreeBSD does not use the BIOS after its
kernel has started. More on this later.</para>
<para>A second reason for translations is the fact that most older
system BIOSes could only handle drives with 17 sectors per track
(the old ST412 standard). Newer system BIOSes usually have a
user-defined drive type (in most cases this is drive type
47).</para>
<warning>
<para>Whatever you do to translations after reading this document,
keep in mind that if you have multiple operating systems on the
same disk, all must use the same translation</para>
</warning>
<para>While on the subject of translations, I have seen one
controller type (but there are probably more like this) offer the
option to logically split a drive in multiple partitions as a BIOS
option. I had select 1 drive == 1 partition because this
controller wrote this info onto the disk. On power-up it read the
info and presented itself to the system based on the info from the
disk.</para>
</sect3>
<sect3>
<title>Spare sectoring</title>
<para>Most ESDI controllers offer the possibility to remap bad
sectors. During/after the low-level format of the disk bad
sectors are marked as such, and a replacement sector is put in
place (logically of course) of the bad one.</para>
<para>In most cases the remapping is done by using N-1 sectors on
each track for actual data storage, and sector N itself is the
spare sector. N is the total number of sectors physically
available on the track. The idea behind this is that the
operating system sees a <quote>perfect</quote> disk without bad sectors. In
the case of FreeBSD this concept is not usable.</para>
<para>The problem is that the translation from
<emphasis>bad</emphasis> to <emphasis>good</emphasis> is performed
by the BIOS of the ESDI controller. FreeBSD, being a true 32 bit
operating system, does not use the BIOS after it has been booted.
Instead, it has device drivers that talk directly to the
hardware.</para>
<para><emphasis>So: do not use spare sectoring, bad block remapping
or whatever it may be called by the controller manufacturer when
you want to use the disk for FreeBSD.</emphasis></para>
</sect3>
<sect3>
<title>Bad block handling</title>
<para>The preceding section leaves us with a problem. The
controller's bad block handling is not usable and still FreeBSD's
filesystems assume perfect media without any flaws. To solve this
problem, FreeBSD use the <command>bad144</command> tool. Bad144
(named after a Digital Equipment standard for bad block handling)
scans a FreeBSD slice for bad blocks. Having found these bad
blocks, it writes a table with the offending block numbers to the
end of the FreeBSD slice.</para>
<para>When the disk is in operation, the disk accesses are checked
against the table read from the disk. Whenever a block number is
requested that is in the <command>bad144</command> list, a
replacement block (also from the end of the FreeBSD slice) is
used. In this way, the <command>bad144</command> replacement
scheme presents <quote>perfect</quote> media to the FreeBSD filesystems.</para>
<para>There are a number of potential pitfalls associated with the
use of <command>bad144</command>. First of all, the slice cannot
have more than 126 bad sectors. If your drive has a high number
of bad sectors, you might need to divide it into multiple FreeBSD
slices each containing less than 126 bad sectors. Stay away from
low-level format programs that mark <emphasis>every</emphasis>
sector of a track as bad when they find a flaw on the track. As
you can imagine, the 126 limit is quickly reached when the
low-level format is done this way.</para>
<para>Second, if the slice contains the root filesystem, the slice
should be within the 1024 cylinder BIOS limit. During the boot
process the bad144 list is read using the BIOS and this only
succeeds when the list is within the 1024 cylinder limit.</para>
<note>
<para>The restriction is not that only the root
<emphasis>filesystem</emphasis> must be within the 1024 cylinder
limit, but rather the entire <emphasis>slice</emphasis> that
contains the root filesystem.</para>
</note>
</sect3>
<sect3>
<title>Kernel configuration</title>
<para>ESDI disks are handled by the same <literal>wd</literal>driver
as IDE and ST412 MFM disks. The <literal>wd</literal> driver
should work for all WD1003 compatible interfaces.</para>
<para>Most hardware is jumperable for one of two different I/O
address ranges and IRQ lines. This allows you to have two wd
type controllers in one system.</para>
<para>When your hardware allows non-standard strappings, you can use
these with FreeBSD as long as you enter the correct info into the
kernel config file. An example from the kernel config file (they
live in <filename>/sys/i386/conf</filename> BTW).</para>
<programlisting># First WD compatible controller
controller wdc0 at isa? port "IO_WD1" bio irq 14 vector wdintr
disk wd0 at wdc0 drive 0
disk wd1 at wdc0 drive 1
# Second WD compatible controller
controller wdc1 at isa? port "IO_WD2" bio irq 15 vector wdintr
disk wd2 at wdc1 drive 0
disk wd3 at wdc1 drive 1</programlisting>
</sect3>
</sect2>
<sect2>
<title>Particulars on ESDI hardware</title>
<sect3>
<title>Adaptec 2320 controllers</title>
<para>I successfully installed FreeBSD onto a ESDI disk controlled
by a ACB-2320. No other operating system was present on the
disk.</para>
<para>To do so I low level formatted the disk using
<command>NEFMT.EXE</command> (<command>ftp</command>able from
<hostid role="fqdn">www.adaptec.com</hostid>) and answered NO to
the question whether the disk should be formatted with a spare
sector on each track. The BIOS on the ACD-2320 was disabled. I
used the <literal>free configurable</literal> option in the system
BIOS to allow the BIOS to boot it.</para>
<para>Before using <command>NEFMT.EXE</command> I tried to format
the disk using the ACB-2320 BIOS built-in formatter. This proved
to be a show stopper, because it did not give me an option to
disable spare sectoring. With spare sectoring enabled the FreeBSD
installation process broke down on the <command>bad144</command>
run.</para>
<para>Please check carefully which
ACB-232<replaceable>xy</replaceable> variant you have. The
<replaceable>x</replaceable> is either <literal>0</literal> or
<literal>2</literal>, indicating a controller without or with a
floppy controller on board.</para>
<para>The <literal>y</literal> is more interesting. It can either
be a blank, a <literal>A-8</literal> or a <literal>D</literal>. A
blank indicates a plain 10 Mbits/second controller. An
<literal>A-8</literal> indicates a 15 Mbits/second controller
capable of handling 52 sectors/track. A <literal>D</literal>
means a 15 Mbits/second controller that can also handle drives
with > 36 sectors/track (also 52?).</para>
<para>All variations should be capable of using 1:1 interleaving.
Use 1:1, FreeBSD is fast enough to handle it.</para>
</sect3>
<sect3>
<title>Western Digital WD1007 controllers</title>
<para>I successfully installed FreeBSD onto a ESDI disk controlled
by a WD1007 controller. To be precise, it was a WD1007-WA2.
Other variations of the WD1007 do exist.</para>
<para>To get it to work, I had to disable the sector translation and
the WD1007's onboard BIOS. This implied I could not use the
low-level formatter built into this BIOS. Instead, I grabbed
<command>WDFMT.EXE</command> from <hostid
role="fqdn">www.wdc.com</hostid> Running this formatted my drive
just fine.</para>
</sect3>
<sect3>
<title>Ultrastor U14F controllers</title>
<para>According to multiple reports from the net, Ultrastor ESDI
boards work OK with FreeBSD. I lack any further info on
particular settings.</para>
</sect3>
</sect2>
<sect2 id="esdi-further-reading">
<title>Further reading</title>
<para>If you intend to do some serious ESDI hacking, you might want to
have the official standard at hand:</para>
<para>The latest ANSI X3T10 committee document is: Enhanced Small
Device Interface (ESDI) [X3.170-1990/X3.170a-1991] [X3T10/792D
Rev 11]</para>
<para>On Usenet the newsgroup <ulink
url="news:comp.periphs">comp.periphs</ulink> is a noteworthy place
to look for more info.</para>
<para>The World Wide Web (WWW) also proves to be a very handy info
source: For info on Adaptec ESDI controllers see <ulink
url="http://www.adaptec.com/"></ulink>. For
info on Western Digital controllers see
<ulink url="http://www.wdc.com/"></ulink>.</para>
</sect2>
<sect2>
<title>Thanks to...</title>
<para>Andrew Gordon for sending me an Adaptec 2320 controller and ESDI
disk for testing.</para>
</sect2>
</sect1>
<sect1 id="scsi">
<title>What is SCSI?</title>
<para><emphasis>Copyright © 1995, &a.wilko;. July 6,
1996.</emphasis></para>
<para>SCSI is an acronym for Small Computer Systems Interface. It is an
ANSI standard that has become one of the leading I/O buses in the
computer industry. The foundation of the SCSI standard was laid by
Shugart Associates (the same guys that gave the world the first mini
floppy disks) when they introduced the SASI bus (Shugart Associates
Standard Interface).</para>
<para>After some time an industry effort was started to come to a more
strict standard allowing devices from different vendors to work
together. This effort was recognized in the ANSI SCSI-1 standard.
The SCSI-1 standard (approximately 1985) is rapidly becoming obsolete. The
current standard is SCSI-2 (see <link
linkend="scsi-further-reading">Further reading</link>), with SCSI-3
on the drawing boards.</para>
<para>In addition to a physical interconnection standard, SCSI defines a
logical (command set) standard to which disk devices must adhere.
This standard is called the Common Command Set (CCS) and was developed
more or less in parallel with ANSI SCSI-1. SCSI-2 includes the
(revised) CCS as part of the standard itself. The commands are
dependent on the type of device at hand. It does not make much sense
of course to define a Write command for a scanner.</para>
<para>The SCSI bus is a parallel bus, which comes in a number of
variants. The oldest and most used is an 8 bit wide bus, with
single-ended signals, carried on 50 wires. (If you do not know what
single-ended means, do not worry, that is what this document is all
about.) Modern designs also use 16 bit wide buses, with differential
signals. This allows transfer speeds of 20Mbytes/second, on cables
lengths of up to 25 meters. SCSI-2 allows a maximum bus width of 32
bits, using an additional cable. Quickly emerging are Ultra SCSI (also
called Fast-20) and Ultra2 (also called Fast-40). Fast-20 is 20
million transfers per second (20 Mbytes/sec on a 8 bit bus), Fast-40
is 40 million transfers per second (40 Mbytes/sec on a 8 bit bus).
Most hard drives sold today are single-ended Ultra SCSI (8 or 16
bits).</para>
<para>Of course the SCSI bus not only has data lines, but also a number
of control signals. A very elaborate protocol is part of the standard
to allow multiple devices to share the bus in an efficient manner. In
SCSI-2, the data is always checked using a separate parity line. In
pre-SCSI-2 designs parity was optional.</para>
<para>In SCSI-3 even faster bus types are introduced, along with a
serial SCSI busses that reduces the cabling overhead and allows a
higher maximum bus length. You might see names like SSA and
fibre channel in this context. None of the serial buses are currently
in widespread use (especially not in the typical FreeBSD environment).
For this reason the serial bus types are not discussed any
further.</para>
<para>As you could have guessed from the description above, SCSI devices
are intelligent. They have to be to adhere to the SCSI standard
(which is over 2 inches thick BTW). So, for a hard disk drive for
instance you do not specify a head/cylinder/sector to address a
particular block, but simply the number of the block you want.
Elaborate caching schemes, automatic bad block replacement etc are all
made possible by this <quote>intelligent device</quote> approach.</para>
<para>On a SCSI bus, each possible pair of devices can communicate.
Whether their function allows this is another matter, but the standard
does not restrict it. To avoid signal contention, the 2 devices have
to arbitrate for the bus before using it.</para>
<para>The philosophy of SCSI is to have a standard that allows
older-standard devices to work with newer-standard ones. So, an old
SCSI-1 device should normally work on a SCSI-2 bus. I say Normally,
because it is not absolutely sure that the implementation of an old
device follows the (old) standard closely enough to be acceptable on a
new bus. Modern devices are usually more well-behaved, because the
standardization has become more strict and is better adhered to by the
device manufacturers.</para>
<para>Generally speaking, the chances of getting a working set of
devices on a single bus is better when all the devices are SCSI-2 or
newer. This implies that you do not have to dump all your old stuff
when you get that shiny 80GB disk: I own a system on which a pre-SCSI-1
disk, a SCSI-2 QIC tape unit, a SCSI-1 helical scan tape unit and 2
SCSI-1 disks work together quite happily. From a performance
standpoint you might want to separate your older and newer (=faster)
devices however. This is especially advantageous if you have an
Ultra160 host adapter where you should separate your U160 devices
from the Fast and Wide SCSI-2 devices.</para>
<sect2>
<title>Components of SCSI</title>
<para>As said before, SCSI devices are smart. The idea is to put the
knowledge about intimate hardware details onto the SCSI device
itself. In this way, the host system does not have to worry about
things like how many heads a hard disks has, or how many tracks
there are on a specific tape device. If you are curious, the
standard specifies commands with which you can query your devices on
their hardware particulars. FreeBSD uses this capability during
boot to check out what devices are connected and whether they need
any special treatment.</para>
<para>The advantage of intelligent devices is obvious: the device
drivers on the host can be made in a much more generic fashion,
there is no longer a need to change (and qualify!) drivers for every
odd new device that is introduced.</para>
<para>For cabling and connectors there is a golden rule: get good
stuff. With bus speeds going up all the time you will save yourself
a lot of grief by using good material.</para>
<para>So, gold plated connectors, shielded cabling, sturdy connector
hoods with strain reliefs etc are the way to go. Second golden rule:
do no use cables longer than necessary. I once spent 3 days hunting
down a problem with a flaky machine only to discover that shortening
the SCSI bus by 1 meter solved the problem. And the original bus
length was well within the SCSI specification.</para>
</sect2>
<sect2>
<title>SCSI bus types</title>
<para>From an electrical point of view, there are two incompatible bus
types: single-ended and differential. This means that there are two
different main groups of SCSI devices and controllers, which cannot
be mixed on the same bus. It is possible however to use special
converter hardware to transform a single-ended bus into a
differential one (and vice versa). The differences between the bus
types are explained in the next sections.</para>
<para>In lots of SCSI related documentation there is a sort of jargon
in use to abbreviate the different bus types. A small list:</para>
<itemizedlist>
<listitem>
<para>FWD: Fast Wide Differential</para>
</listitem>
<listitem>
<para>FND: Fast Narrow Differential</para>
</listitem>
<listitem>
<para>SE: Single Ended</para>
</listitem>
<listitem>
<para>FN: Fast Narrow</para>
</listitem>
<listitem>
<para>etc.</para>
</listitem>
</itemizedlist>
<para>With a minor amount of imagination one can usually imagine what
is meant.</para>
<para>Wide is a bit ambiguous, it can indicate 16 or 32 bit buses. As
far as I know, the 32 bit variant is not (yet) in use, so wide
normally means 16 bit.</para>
<para>Fast means that the timing on the bus is somewhat different, so
that on a narrow (8 bit) bus 10 Mbytes/sec are possible instead of 5
Mbytes/sec for <quote>slow</quote> SCSI. As discussed before, bus speeds of 20
and 40 million transfers/second are also emerging (Fast-20 == Ultra
SCSI and Fast-40 == Ultra2 SCSI).</para>
<note>
<para>The data lines > 8 are only used for data transfers and
device addressing. The transfers of commands and status messages
etc are only performed on the lowest 8 data lines. The standard
allows narrow devices to operate on a wide bus. The usable bus
width is negotiated between the devices. You have to watch your
device addressing closely when mixing wide and narrow.</para>
</note>
<sect3>
<title>Single ended buses</title>
<para>A single-ended SCSI bus uses signals that are either 5 Volts
or 0 Volts (indeed, TTL levels) and are relative to a COMMON
ground reference. A singled ended 8 bit SCSI bus has
approximately 25 ground lines, who are all tied to a single <quote>rail</quote>
on all devices. A standard single ended bus has a maximum length
of 6 meters. If the same bus is used with fast-SCSI devices, the
maximum length allowed drops to 3 meters. Fast-SCSI means that
instead of 5Mbytes/sec the bus allows 10Mbytes/sec
transfers.</para>
<para>Fast-20 (Ultra SCSI) and Fast-40 allow for 20 and 40 million
transfers/second respectively. So, F20 is 20 Mbytes/second on a 8
bit bus, 40 Mbytes/second on a 16 bit bus etc. For F20 the max
bus length is 1.5 meters, for F40 it becomes 0.75 meters. Be
aware that F20 is pushing the limits quite a bit, so you will
quickly find out if your SCSI bus is electrically sound.</para>
<note>
<para>If some devices on your bus use <quote>fast</quote> to communicate your
bus must adhere to the length restrictions for fast
buses!</para>
</note>
<para>It is obvious that with the newer fast-SCSI devices the bus
length can become a real bottleneck. This is why the differential
SCSI bus was introduced in the SCSI-2 standard.</para>
<para>For connector pinning and connector types please refer to the
SCSI-2 standard (see <link linkend="scsi-further-reading">Further
reading</link>) itself, connectors etc are listed there in
painstaking detail.</para>
<para>Beware of devices using non-standard cabling. For instance
Apple uses a 25pin D-type connecter (like the one on serial ports
and parallel printers). Considering that the official SCSI bus
needs 50 pins you can imagine the use of this connector needs some
<quote>creative cabling</quote>. The reduction of the number of ground wires
they used is a bad idea, you better stick to 50 pins cabling in
accordance with the SCSI standard. For Fast-20 and 40 do not even
think about buses like this.</para>
</sect3>
<sect3>
<title>Differential buses</title>
<para>A differential SCSI bus has a maximum length of 25 meters.
Quite a difference from the 3 meters for a single-ended fast-SCSI
bus. The idea behind differential signals is that each bus signal
has its own return wire. So, each signal is carried on a
(preferably twisted) pair of wires. The voltage difference
between these two wires determines whether the signal is asserted
or de-asserted. To a certain extent the voltage difference
between ground and the signal wire pair is not relevant (do not
try 10 kVolts though).</para>
<para>It is beyond the scope of this document to explain why this
differential idea is so much better. Just accept that
electrically seen the use of differential signals gives a much
better noise margin. You will normally find differential buses in
use for inter-cabinet connections. Because of the lower cost
single ended is mostly used for shorter buses like inside
cabinets.</para>
<para>There is nothing that stops you from using differential stuff
with FreeBSD, as long as you use a controller that has device
driver support in FreeBSD. As an example, Adaptec marketed the
AHA1740 as a single ended board, whereas the AHA1744 was
differential. The software interface to the host is identical for
both.</para>
</sect3>
<sect3>
<title>Terminators</title>
<para>Terminators in SCSI terminology are resistor networks that are
used to get a correct impedance matching. Impedance matching is
important to get clean signals on the bus, without reflections or
ringing. If you once made a long distance telephone call on a bad
line you probably know what reflections are. With 20Mbytes/sec
traveling over your SCSI bus, you do not want signals echoing
back.</para>
<para>Terminators come in various incarnations, with more or less
sophisticated designs. Of course, there are internal and external
variants. Many SCSI devices come with a number of sockets in
which a number of resistor networks can (must be!) installed. If
you remove terminators from a device, carefully store them. You
will need them when you ever decide to reconfigure your SCSI bus.
There is enough variation in even these simple tiny things to make
finding the exact replacement a frustrating business. There are
also SCSI devices that have a single jumper to enable or disable a
built-in terminator. There are special terminators you can stick
onto a flat cable bus. Others look like external connectors, or a
connector hood without a cable. So, lots of choice as you can
see.</para>
<para>There is much debate going on if and when you should switch
from simple resistor (passive) terminators to active terminators.
Active terminators contain slightly more elaborate circuit to give
cleaner bus signals. The general consensus seems to be that the
usefulness of active termination increases when you have long
buses and/or fast devices. If you ever have problems with your
SCSI buses you might consider trying an active terminator. Try to
borrow one first, they reputedly are quite expensive.</para>
<para>Please keep in mind that terminators for differential and
single-ended buses are not identical. You should <emphasis>not
mix</emphasis> the two variants.</para>
<para>OK, and now where should you install your terminators? This is
by far the most misunderstood part of SCSI. And it is by far the
simplest. The rule is: <emphasis>every single line on the SCSI
bus has 2 (two) terminators, one at each end of the
bus.</emphasis> So, two and not one or three or whatever. Do
yourself a favor and stick to this rule. It will save you endless
grief, because wrong termination has the potential to introduce
highly mysterious bugs. (Note the <quote>potential</quote> here;
the nastiest part is that it may or may not work.)</para>
<para>A common pitfall is to have an internal (flat) cable in a
machine and also an external cable attached to the controller. It
seems almost everybody forgets to remove the terminators from the
controller. The terminator must now be on the last external
device, and not on the controller! In general, every
reconfiguration of a SCSI bus must pay attention to this.</para>
<note>
<para>Termination is to be done on a per-line basis. This means
if you have both narrow and wide buses connected to the same
host adapter, you need to enable termination on the higher 8
bits of the bus on the adapter (as well as the last devices on
each bus, of course).</para>
</note>
<para>What I did myself is remove all terminators from my SCSI
devices and controllers. I own a couple of external terminators,
for both the Centronics-type external cabling and for the internal
flat cable connectors. This makes reconfiguration much
easier.</para>
<para>On modern devices, sometimes integrated terminators are used.
These things are special purpose integrated circuits that can be
enabled or disabled with a control pin. It is not necessary to
physically remove them from a device. You may find them on newer
host adapters, sometimes they are software configurable, using
some sort of setup tool. Some will even auto-detect the cables
attached to the connectors and automatically set up the
termination as necessary. At any rate, consult your
documentation!</para>
</sect3>
<sect3>
<title>Terminator power</title>
<para>The terminators discussed in the previous chapter need power
to operate properly. On the SCSI bus, a line is dedicated to this
purpose. So, simple huh?</para>
<para>Not so. Each device can provide its own terminator power to
the terminator sockets it has on-device. But if you have external
terminators, or when the device supplying the terminator power to
the SCSI bus line is switched off you are in trouble.</para>
<para>The idea is that initiators (these are devices that initiate
actions on the bus, a discussion follows) must supply terminator
power. All SCSI devices are allowed (but not required) to supply
terminator power.</para>
<para>To allow for un-powered devices on a bus, the terminator power
must be supplied to the bus via a diode. This prevents the
backflow of current to un-powered devices.</para>
<para>To prevent all kinds of nastiness, the terminator power is
usually fused. As you can imagine, fuses might blow. This can,
but does not have to, lead to a non functional bus. If multiple
devices supply terminator power, a single blown fuse will not put
you out of business. A single supplier with a blown fuse
certainly will. Clever external terminators sometimes have a LED
indication that shows whether terminator power is present.</para>
<para>In newer designs auto-restoring fuses that <quote>reset</quote> themselves
after some time are sometimes used.</para>
</sect3>
<sect3>
<title>Device addressing</title>
<para>Because the SCSI bus is, ehh, a bus there must be a way to
distinguish or address the different devices connected to
it.</para>
<para>This is done by means of the SCSI or target ID. Each device
has a unique target ID. You can select the ID to which a device
must respond using a set of jumpers, or a dip switch, or something
similar. Some SCSI host adapters let you change the target ID
from the boot menu. (Yet some others will not let you change the
ID from 7.) Consult the documentation of your device for more
information.</para>
<para>Beware of multiple devices configured to use the same ID.
Chaos normally reigns in this case. A pitfall is that one of the
devices sharing the same ID sometimes even manages to answer to
I/O requests!</para>
<para>For an 8 bit bus, a maximum of 8 targets is possible. The
maximum is 8 because the selection is done bitwise using the 8
data lines on the bus. For wide buses this increases to the
number of data lines (usually 16).</para>
<note>
<para>A narrow SCSI device can not communicate with a SCSI device
with a target ID larger than 7. This means it is generally not
a good idea to move your SCSI host adapter's target ID to
something higher than 7 (or your CDROM will stop
working).</para>
</note>
<para>The higher the SCSI target ID, the higher the priority the
devices has. When it comes to arbitration between devices that
want to use the bus at the same time, the device that has the
highest SCSI ID will win. This also means that the SCSI host
adapter usually uses target ID 7. Note however that the lower 8
IDs have higher priorities than the higher 8 IDs on a wide-SCSI
bus. Thus, the order of target IDs is: [7 6 .. 1 0 15 14 .. 9 8]
on a wide-SCSI system. (If you are wondering why the lower 8
have higher priority, read the previous paragraph for a
hint.)</para>
<para>For a further subdivision, the standard allows for Logical
Units or LUNs for short. A single target ID may have multiple
LUNs. For example, a tape device including a tape changer may
have LUN 0 for the tape device itself, and LUN 1 for the tape
changer. In this way, the host system can address each of the
functional units of the tape changer as desired.</para>
</sect3>
<sect3>
<title>Bus layout</title>
<para>SCSI buses are linear. So, not shaped like Y-junctions, star
topologies, rings, cobwebs or whatever else people might want to
invent. One of the most common mistakes is for people with
wide-SCSI host adapters to connect devices on all three connecters
(external connector, internal wide connector, internal narrow
connector). Do not do that. It may appear to work if you are
really lucky, but I can almost guarantee that your system will
stop functioning at the most unfortunate moment (this is also
known as <quote>Murphy's law</quote>).</para>
<para>You might notice that the terminator issue discussed earlier
becomes rather hairy if your bus is not linear. Also, if you have
more connectors than devices on your internal SCSI cable, make
sure you attach devices on connectors on both ends instead of
using the connectors in the middle and let one or both ends
dangle. This will screw up the termination of the bus.</para>
<para>The electrical characteristics, its noise margins and
ultimately the reliability of it all are tightly related to linear
bus rule.</para>
<para><emphasis>Stick to the linear bus rule!</emphasis></para>
</sect3>
</sect2>
<sect2>
<title>Using SCSI with FreeBSD</title>
<sect3>
<title>About translations, BIOSes and magic...</title>
<para>As stated before, you should first make sure that you have a
electrically sound bus.</para>
<para>When you want to use a SCSI disk on your PC as boot disk, you
must aware of some quirks related to PC BIOSes. The PC BIOS in
its first incarnation used a low level physical interface to the
hard disk. So, you had to tell the BIOS (using a setup tool or a
BIOS built-in setup) how your disk physically looked like. This
involved stating number of heads, number of cylinders, number of
sectors per track, obscure things like precompensation and reduced
write current cylinder etc.</para>
<para>One might be inclined to think that since SCSI disks are smart
you can forget about this. Alas, the arcane setup issue is still
present today. The system BIOS needs to know how to access your
SCSI disk with the head/cyl/sector method in order to load the
FreeBSD kernel during boot.</para>
<para>The SCSI host adapter or SCSI controller you have put in your
AT/EISA/PCI/whatever bus to connect your disk therefore has its
own on-board BIOS. During system startup, the SCSI BIOS takes
over the hard disk interface routines from the system BIOS. To
fool the system BIOS, the system setup is normally set to No hard
disk present. Obvious, is it not?</para>
<para>The SCSI BIOS itself presents to the system a so called
<emphasis>translated</emphasis> drive. This means that a fake
drive table is constructed that allows the PC to boot the drive.
This translation is often (but not always) done using a pseudo
drive with 64 heads and 32 sectors per track. By varying the
number of cylinders, the SCSI BIOS adapts to the actual drive
size. It is useful to note that 32 * 64 / 2 = the size of your
drive in megabytes. The division by 2 is to get from disk blocks
that are normally 512 bytes in size to Kbytes.</para>
<para>Right. All is well now?! No, it is not. The system BIOS has
another quirk you might run into. The number of cylinders of a
bootable hard disk cannot be greater than 1024. Using the
translation above, this is a show-stopper for disks greater than 1
GB. With disk capacities going up all the time this is causing
problems.</para>
<para>Fortunately, the solution is simple: just use another
translation, e.g. with 128 heads instead of 32. In most cases new
SCSI BIOS versions are available to upgrade older SCSI host
adapters. Some newer adapters have an option, in the form of a
jumper or software setup selection, to switch the translation the
SCSI BIOS uses.</para>
<para>It is very important that <emphasis>all</emphasis> operating
systems on the disk use the <emphasis>same translation</emphasis>
to get the right idea about where to find the relevant partitions.
So, when installing FreeBSD you must answer any questions about
heads/cylinders etc using the translated values your host adapter
uses.</para>
<para>Failing to observe the translation issue might lead to
un-bootable systems or operating systems overwriting each others
partitions. Using fdisk you should be able to see all
partitions.</para>
<para>You might have heard some talk of <quote>lying</quote> devices?
Older FreeBSD kernels used to report the geometry of SCSI disks
when booting. An example from one of my systems:</para>
<screen>aha0 targ 0 lun 0: <MICROP 1588-15MB1057404HSP4>
da0: 636MB (1303250 total sec), 1632 cyl, 15 head, 53 sec, bytes/sec 512</screen>
<para>Newer kernels usually do not report this information.
e.g.</para>
<screen>(bt0:0:0): "SEAGATE ST41651 7574" type 0 fixed SCSI 2
da0(bt0:0:0): Direct-Access 1350MB (2766300 512 byte sectors)</screen>
<para>Why has this changed?</para>
<para>This info is retrieved from the SCSI disk itself. Newer disks
often use a technique called zone bit recording. The idea is that
on the outer cylinders of the drive there is more space so more
sectors per track can be put on them. This results in disks that
have more tracks on outer cylinders than on the inner cylinders
and, last but not least, have more capacity. You can imagine that
the value reported by the drive when inquiring about the geometry
now becomes suspect at best, and nearly always misleading. When
asked for a geometry, it is nearly always better to supply the
geometry used by the BIOS, or <emphasis>if the BIOS is never going
to know about this disk</emphasis>, (e.g. it is not a booting
disk) to supply a fictitious geometry that is convenient.</para>
</sect3>
<sect3>
<title>SCSI subsystem design</title>
<para>FreeBSD uses a layered SCSI subsystem. For each different
controller card a device driver is written. This driver knows all
the intimate details about the hardware it controls. The driver
has a interface to the upper layers of the SCSI subsystem through
which it receives its commands and reports back any status.</para>
<para>On top of the card drivers there are a number of more generic
drivers for a class of devices. More specific: a driver for tape
devices (abbreviation: sa, for serial access),
magnetic disks (da, for direct access), CDROMs (cd) etc.
In case you are wondering where you can find this stuff, it all
lives in <filename>/sys/cam/scsi</filename>. See the man pages in
section 4 for more details.</para>
<para>The multi level design allows a decoupling of low-level bit
banging and more high level stuff. Adding support for another
piece of hardware is a much more manageable problem.</para>
</sect3>
<sect3>
<title>Kernel configuration</title>
<para>Dependent on your hardware, the kernel configuration file must
contain one or more lines describing your host adapter(s). This
includes I/O addresses, interrupts etc. Consult the manual page for
your adapter driver to get more info. Apart from that, check out
<filename>/sys/i386/conf/LINT</filename> for an overview of a
kernel config file. <filename>LINT</filename> contains every
possible option you can dream of. It does
<emphasis>not</emphasis> imply <filename>LINT</filename> will
actually get you to a working kernel at all.</para>
<para>Although it is probably stating the obvious: the kernel config
file should reflect your actual hardware setup. So, interrupts,
I/O addresses etc must match the kernel config file. During
system boot messages will be displayed to indicate whether the
configured hardware was actually found.</para>
<note>
<para>Note that most of the EISA/PCI drivers (namely
<devicename>ahb</devicename>, <devicename>ahc</devicename>,
<devicename>ncr</devicename> and <devicename>amd</devicename>
will automatically obtain the correct parameters from the host
adapters themselves at boot time; thus, you just need to write,
for instance, <literal>controller ahc0</literal>.</para>
</note>
<para>An example loosely based on the FreeBSD 2.2.5-Release kernel
config file <filename>LINT</filename> with some added comments
(between []):</para>
<programlisting># SCSI host adapters: `aha', `ahb', `aic', `bt', `nca'
#
# aha: Adaptec 154x
# ahb: Adaptec 174x
# ahc: Adaptec 274x/284x/294x
# aic: Adaptec 152x and sound cards using the Adaptec AIC-6360 (slow!)
# amd: AMD 53c974 based SCSI cards (e.g., Tekram DC-390 and 390T)
# bt: Most Buslogic controllers
# nca: ProAudioSpectrum cards using the NCR 5380 or Trantor T130
# ncr: NCR/Symbios 53c810/815/825/875 etc based SCSI cards
# uha: UltraStore 14F and 34F
# sea: Seagate ST01/02 8 bit controller (slow!)
# wds: Western Digital WD7000 controller (no scatter/gather!).
#
[For an Adaptec AHA274x/284x/294x/394x etc controller]
controller ahc0
[For an NCR/Symbios 53c875 based controller]
controller ncr0
[For an Ultrastor adapter]
controller uha0 at isa? port "IO_UHA0" bio irq ? drq 5 vector uhaintr
# Map SCSI buses to specific SCSI adapters
controller scbus0 at ahc0
controller scbus2 at ncr0
controller scbus1 at uha0
# The actual SCSI devices
disk da0 at scbus0 target 0 unit 0 [SCSI disk 0 is at scbus 0, LUN 0]
disk da1 at scbus0 target 1 [implicit LUN 0 if omitted]
disk da2 at scbus1 target 3 [SCSI disk on the uha0]
disk da3 at scbus2 target 4 [SCSI disk on the ncr0]
tape sa1 at scbus0 target 6 [SCSI tape at target 6]
device cd0 at scbus? [the first ever CDROM found, no wiring]</programlisting>
<para>The example above tells the kernel to look for a ahc (Adaptec
274x) controller, then for an NCR/Symbios board, and so on. The
lines following the controller specifications tell the kernel to
configure specific devices but <emphasis>only</emphasis> attach
them when they match the target ID and LUN specified on the
corresponding bus.</para>
<para>Wired down devices get <quote>first shot</quote> at the unit
numbers so the first non <quote>wired down</quote> device, is
allocated the unit number one greater than the highest
<quote>wired down</quote> unit number for that kind of device. So,
if you had a SCSI tape at target ID 2 it would be configured as
sa2, as the tape at target ID 6 is wired down to unit number
1.</para>
<note>
<para>Wired down devices need not be found to get their unit
number. The unit number for a wired down device is reserved for
that device, even if it is turned off at boot time. This allows
the device to be turned on and brought on-line at a later time,
without rebooting. Notice that a device's unit number has
<emphasis>no</emphasis> relationship with its target ID on the
SCSI bus.</para>
</note>
<para>Below is another example of a kernel config file as used by
FreeBSD version < 2.0.5. The difference with the first example
is that devices are not <quote>wired down</quote>. <quote>Wired
down</quote> means that you specify which SCSI target belongs to
which device.</para>
<para>A kernel built to the config file below will attach the first
SCSI disk it finds to da0, the second disk to da1 etc. If you ever
removed or added a disk, all other devices of the same type (disk
in this case) would <quote>move around</quote>. This implies you have to
change <filename>/etc/fstab</filename> each time.</para>
<para>Although the old style still works, you are
<emphasis>strongly</emphasis> recommended to use this new feature.
It will save you a lot of grief whenever you shift your hardware
around on the SCSI buses. So, when you re-use your old trusty
config file after upgrading from a pre-FreeBSD2.0.5.R system check
this out.</para>
<programlisting>[driver for Adaptec 174x]
controller ahb0 at isa? bio irq 11 vector ahbintr
[for Adaptec 154x]
controller aha0 at isa? port "IO_AHA0" bio irq 11 drq 5 vector ahaintr
[for Seagate ST01/02]
controller sea0 at isa? bio irq 5 iomem 0xc8000 iosiz 0x2000 vector seaintr
controller scbus0
device da0 [support for 4 SCSI harddisks, da0 up da3]
device sa0 [support for 2 SCSI tapes]
[for the CDROM]
device cd0 #Only need one of these, the code dynamically grows</programlisting>
<para>Both examples support SCSI disks. If during boot more devices
of a specific type (e.g. da disks) are found than are configured
in the booting kernel, the system will simply allocate more
devices, incrementing the unit number starting at the last number
<quote>wired down</quote>. If there are no <quote>wired
down</quote> devices then counting starts at unit 0.</para>
<para>Use <command>man 4 scsi</command> to check for the latest info
on the SCSI subsystem. For more detailed info on host adapter
drivers use e.g., <command>man 4 ahc</command> for info on the
Adaptec 294x driver.</para>
</sect3>
<sect3>
<title>Tuning your SCSI kernel setup</title>
<para>Experience has shown that some devices are slow to respond to
INQUIRY commands after a SCSI bus reset (which happens at boot
time). An INQUIRY command is sent by the kernel on boot to see
what kind of device (disk, tape, CDROM etc.) is connected to a
specific target ID. This process is called device probing by the
way.</para>
<para>To work around the <quote>slow response</quote> problem, FreeBSD allows a
tunable delay time before the SCSI devices are probed following a
SCSI bus reset. You can set this delay time in your kernel
configuration file using a line like:</para>
<programlisting>options SCSI_DELAY=15 #Be pessimistic about Joe SCSI device</programlisting>
<para>This line sets the delay time to 15 seconds. On my own system
I had to use 3 seconds minimum to get my trusty old CDROM drive
to be recognized. Start with a high value (say 30 seconds or so)
when you have problems with device recognition. If this helps,
tune it back until it just stays working.</para>
</sect3>
<sect3 id="scsi-rogue-devices">
<title>Rogue SCSI devices</title>
<para>Although the SCSI standard tries to be complete and concise,
it is a complex standard and implementing things correctly is no
easy task. Some vendors do a better job then others.</para>
<para>This is exactly where the <quote>rogue</quote> devices come
into view. Rogues are devices that are recognized by the FreeBSD
kernel as behaving slightly (...) non-standard. Rogue devices are
reported by the kernel when booting. An example for two of my
cartridge tape units:</para>
<screen>Feb 25 21:03:34 yedi /kernel: ahb0 targ 5 lun 0: <TANDBERG TDC 3600 -06:>
Feb 25 21:03:34 yedi /kernel: sa0: Tandberg tdc3600 is a known rogue
Mar 29 21:16:37 yedi /kernel: aha0 targ 5 lun 0: <ARCHIVE VIPER 150 21247-005>
Mar 29 21:16:37 yedi /kernel: sa1: Archive Viper 150 is a known rogue </screen>
<para>For instance, there are devices that respond to all LUNs on a
certain target ID, even if they are actually only one device. It
is easy to see that the kernel might be fooled into believing that
there are 8 LUNs at that particular target ID. The confusion this
causes is left as an exercise to the reader.</para>
<para>The SCSI subsystem of FreeBSD recognizes devices with bad
habits by looking at the INQUIRY response they send when probed.
Because the INQUIRY response also includes the version number of
the device firmware, it is even possible that for different
firmware versions different workarounds are used. See e.g.
<filename>/sys/cam/scsi/scsi_sa.c</filename> and
<filename>/sys/cam/scsi/scsi_all.c</filename> for more info on how
this is done.</para>
<para>This scheme works fine, but keep in mind that it of course
only works for devices that are known to be weird. If you are the
first to connect your bogus Mumbletech SCSI CDROM you might be
the one that has to define which workaround is needed.</para>
<para>After you got your Mumbletech working, please send the
required workaround to the FreeBSD development team for inclusion
in the next release of FreeBSD. Other Mumbletech owners will be
grateful to you.</para>
</sect3>
<sect3>
<title>Multiple LUN devices</title>
<para>In some cases you come across devices that use multiple
logical units (LUNs) on a single SCSI ID. In most cases FreeBSD
only probes devices for LUN 0. An example are so called bridge
boards that connect 2 non-SCSI hard disks to a SCSI bus (e.g. an
Emulex MD21 found in old Sun systems).</para>
<para>This means that any devices with LUNs != 0 are not normally
found during device probe on system boot. To work around this
problem you must add an appropriate entry in /sys/cam/scsi
and rebuild your kernel.</para>
<para>Look for a struct that is initialized like below:
(FIXME: which file? Do these entries still exist in this form
now that we use CAM?)</para>
<programlisting>{
T_DIRECT, T_FIXED, "MAXTOR", "XT-4170S", "B5A",
"mx1", SC_ONE_LU
}</programlisting>
<para>For your Mumbletech BRIDGE2000 that has more than one LUN, acts
as a SCSI disk and has firmware revision 123 you would add
something like:</para>
<programlisting>{
T_DIRECT, T_FIXED, "MUMBLETECH", "BRIDGE2000", "123",
"da", SC_MORE_LUS
}</programlisting>
<para>The kernel on boot scans the inquiry data it receives against
the table and acts accordingly. See the source for more
info.</para>
</sect3>
<sect3>
<title>Tagged command queuing</title>
<para>Modern SCSI devices, particularly magnetic disks,
support what is called tagged command queuing (TCQ).</para>
<para>In a nutshell, TCQ allows the device to have multiple I/O
requests outstanding at the same time. Because the device is
intelligent, it can optimize its operations (like head
positioning) based on its own request queue. On SCSI devices
like RAID (Redundant Array of Independent Disks) arrays the TCQ
function is indispensable to take advantage of the device's
inherent parallelism.</para>
<para>Each I/O request is uniquely identified by a <quote>tag</quote>
(hence the name tagged command queuing) and this tag is used by
FreeBSD to see which I/O in the device drivers queue is reported
as complete by the device.</para>
<para>It should be noted however that TCQ requires device driver
support and that some devices implemented it <quote>not quite
right</quote> in their firmware. This problem bit me once, and it
leads to highly mysterious problems. In such cases, try to
disable TCQ.</para>
</sect3>
<sect3>
<title>Bus-master host adapters</title>
<para>Most, but not all, SCSI host adapters are bus mastering
controllers. This means that they can do I/O on their own without
putting load onto the host CPU for data movement.</para>
<para>This is of course an advantage for a multitasking operating
system like FreeBSD. It must be noted however that there might be
some rough edges.</para>
<para>For instance an Adaptec 1542 controller can be set to use
different transfer speeds on the host bus (ISA or AT in this
case). The controller is settable to different rates because not
all motherboards can handle the higher speeds. Problems like
hang-ups, bad data etc might be the result of using a higher data
transfer rate then your motherboard can stomach.</para>
<para>The solution is of course obvious: switch to a lower data
transfer rate and try if that works better.</para>
<para>In the case of a Adaptec 1542, there is an option that can be
put into the kernel config file to allow dynamic determination of
the right, read: fastest feasible, transfer rate. This option is
disabled by default:</para>
<programlisting>options "TUNE_1542" #dynamic tune of bus DMA speed</programlisting>
<para>Check the manual pages for the host adapter that you use. Or
better still, use the ultimate documentation (read: driver
source).</para>
</sect3>
</sect2>
<sect2>
<title>Tracking down problems</title>
<para>The following list is an attempt to give a guideline for the
most common SCSI problems and their solutions. It is by no means
complete.</para>
<itemizedlist>
<listitem>
<para>Check for loose connectors and cables.</para>
</listitem>
<listitem>
<para>Check and double check the location and number of your
terminators.</para>
</listitem>
<listitem>
<para>Check if your bus has at least one supplier of terminator
power (especially with external terminators.</para>
</listitem>
<listitem>
<para>Check if no double target IDs are used.</para>
</listitem>
<listitem>
<para>Check if all devices to be used are powered up.</para>
</listitem>
<listitem>
<para>Make a minimal bus config with as little devices as
possible.</para>
</listitem>
<listitem>
<para>If possible, configure your host adapter to use slow bus
speeds.</para>
</listitem>
<listitem>
<para>Disable tagged command queuing to make things as simple as
possible (for a NCR host adapter based system see man
ncrcontrol)</para>
</listitem>
<listitem>
<para>If you can compile a kernel, make one with the
<literal>SCSIDEBUG</literal> option, and try accessing the
device with debugging turned on for that device. If your device
does not even probe at startup, you may have to define the
address of the device that is failing, and the desired debug
level in <filename>/sys/cam/cam_debug.h</filename>. If it
probes but just does not work, you can use the
&man.camcontrol.8; command to dynamically set a debug level to
it in a running kernel (if <literal>CAMDEBUG</literal> is
defined). This will give you <emphasis>copious</emphasis>
debugging output with which to confuse the gurus. See
<command>man camcontrol</command> for more exact information. Also
look at <command>man 4 pass</command>.</para>
</listitem>
</itemizedlist>
</sect2>
<sect2 id="scsi-further-reading">
<title>Further reading</title>
<para>If you intend to do some serious SCSI hacking, you might want to
have the official standard at hand:</para>
<para>Approved American National Standards can be purchased from
ANSI at
<address>
<otheraddr>13th Floor</otheraddr>
<street>11 West 42nd Street</street>
<city>New York</city>
<state>NY</state> <postcode>10036</postcode>
Sales Dept: <phone>(212) 642-4900</phone>
</address>
</para>
<para>You can also buy many ANSI
standards and most committee draft documents from Global
Engineering Documents,
<address>
<street>15 Inverness Way East</street>
<city>Englewood</city>
<state>CO</state>, <postcode>80112-5704</postcode>
Phone: <phone>(800) 854-7179</phone>
Outside USA and Canada: <phone>(303) 792-2181</phone>
Fax: <fax>(303) 792- 2192</fax>
</address>
</para>
<para>Many X3T10 draft documents are available electronically on the
SCSI BBS (719-574-0424) and on the <hostid
role="fqdn">ncrinfo.ncr.com</hostid> anonymous FTP site.</para>
<para>Latest X3T10 committee documents are:</para>
<itemizedlist>
<listitem>
<para>AT Attachment (ATA or IDE) [X3.221-1994]
(<emphasis>Approved</emphasis>)</para>
</listitem>
<listitem>
<para>ATA Extensions (ATA-2) [X3T10/948D Rev 2i]</para>
</listitem>
<listitem>
<para>Enhanced Small Device Interface (ESDI)
[X3.170-1990/X3.170a-1991]
(<emphasis>Approved</emphasis>)</para>
</listitem>
<listitem>
<para>Small Computer System Interface — 2 (SCSI-2)
[X3.131-1994] (<emphasis>Approved</emphasis>)</para>
</listitem>
<listitem>
<para>SCSI-2 Common Access Method Transport and SCSI Interface
Module (CAM) [X3T10/792D Rev 11]</para>
</listitem>
</itemizedlist>
<para>Other publications that might provide you with additional
information are:</para>
<itemizedlist>
<listitem>
<para><quote>SCSI: Understanding the Small Computer System
Interface</quote>, written by NCR Corporation. Available from:
Prentice Hall, Englewood Cliffs, NJ, 07632 Phone: (201) 767-5937
ISBN 0-13-796855-8</para>
</listitem>
<listitem>
<para><quote>Basics of SCSI</quote>, a SCSI tutorial written by
Ancot Corporation Contact Ancot for availability information at:
Phone: (415) 322-5322 Fax: (415) 322-0455</para>
</listitem>
<listitem>
<para><quote>SCSI Interconnection Guide Book</quote>, an AMP
publication (dated 4/93, Catalog 65237) that lists the various
SCSI connectors and suggests cabling schemes. Available from
AMP at (800) 522-6752 or (717) 564-0100</para>
</listitem>
<listitem>
<para><quote>Fast Track to SCSI</quote>, A Product Guide written by
Fujitsu. Available from: Prentice Hall, Englewood Cliffs, NJ,
07632 Phone: (201) 767-5937 ISBN 0-13-307000-X</para>
</listitem>
<listitem>
<para><quote>The SCSI Bench Reference</quote>, <quote>The SCSI
Encyclopedia</quote>, and the <quote>SCSI Tutor</quote>, ENDL
Publications, 14426 Black Walnut Court, Saratoga CA, 95070
Phone: (408) 867-6642</para>
</listitem>
<listitem>
<para><quote>Zadian SCSI Navigator</quote> (quick ref. book) and
<quote>Discover the Power of SCSI</quote> (First book along with
a one-hour video and tutorial book), Zadian Software, Suite 214,
1210 S. Bascom Ave., San Jose, CA 92128, (408) 293-0800</para>
</listitem>
</itemizedlist>
<para>On Usenet the newsgroups <ulink
url="news:comp.periphs.scsi">comp.periphs.scsi</ulink> and <ulink
url="news:comp.periphs">comp.periphs</ulink> are noteworthy places
to look for more info. You can also find the <ulink
url="http://scsifaq.org:9080/scsi_faq/scsifaq.html">SCSI-FAQ</ulink>
there, which is posted periodically.</para>
<para>Most major SCSI device and host adapter suppliers operate FTP
sites and/or BBS systems. They may be valuable sources of
information about the devices you own.</para>
</sect2>
</sect1>
<sect1 id="hw-storage-controllers">
<title>* Disk/tape controllers</title>
<sect2>
<title>* SCSI</title>
<para></para>
</sect2>
<sect2>
<title>* IDE</title>
<para></para>
</sect2>
<sect2>
<title>* Floppy</title>
<para></para>
</sect2>
</sect1>
<sect1>
<title>Hard drives</title>
<sect2>
<title>SCSI hard drives</title>
<para><emphasis>Contributed by &a.asami;. 17 February
1998.</emphasis></para>
<para>As mentioned in the <link linkend="scsi">SCSI</link> section,
virtually all SCSI hard drives sold today are SCSI-2 compliant and
thus will work fine as long as you connect them to a supported SCSI
host adapter. Most problems people encounter are either due to
badly designed cabling (cable too long, star topology, etc.),
insufficient termination, or defective parts. Please refer to the
<link linkend="scsi">SCSI</link> section first if your SCSI hard
drive is not working. However, there are a couple of things you may
want to take into account before you purchase SCSI hard drives for
your system.</para>
<sect3>
<title>Rotational speed</title>
<para>Rotational speeds of SCSI drives sold today range from around
4,500RPM to 15,000RPM. Most of them are either 7,200RPM or
10,000RPM, with 15,000RPM becoming affordable (June 2002).
Even though the 10,000RPM drives can generally transfer
data faster, they run considerably hotter than their 7,200RPM
counterparts. A large fraction of today's disk drive malfunctions
are heat-related. If you do not have very good cooling in your PC
case, you may want to stick with 7,200RPM or slower drives.</para>
<para>Note that newer drives, with higher areal recording densities,
can deliver much more bits per rotation than older ones. Today's
top-of-line 7,200RPM drives can sustain a throughput comparable to
10,000RPM drives of one or two model generations ago. The number
to find on the spec sheet for bandwidth is <quote>internal data
(or transfer) rate</quote>. It is usually in megabits/sec so
divide it by 8 and you will get the rough approximation of how much
megabytes/sec you can get out of the drive.</para>
<para>(If you are a speed maniac and want a 15,000RPM drive for your
cute little PC, be my guest; however, those drives become
extremely hot. Do not even think about it if you do not have a fan
blowing air <emphasis>directly at</emphasis> the drive or a
properly ventilated disk enclosure.)</para>
<para>Obviously, the latest 15,000RPM drives and 10,000RPM drives can
deliver more data than the latest 7,200RPM drives, so if absolute
bandwidth is the necessity for your applications, you have little
choice but to get the faster drives. Also, if you need low
latency, faster drives are better; not only do they usually have
lower average seek times, but also the rotational delay is one
place where slow-spinning drives can never beat a faster one.
(The average rotational latency is half the time it takes to
rotate the drive once; thus, it is 2 milliseconds for 15,000RPM,
3ms for 10,000RPM
drives, 4.2ms for 7,200RPM drives and 5.6ms for 5,400RPM drives.)
Latency is seek time plus rotational delay. Make sure you
understand whether you need low latency or more accesses per
second, though; in the latter case (e.g., news servers), it may
not be optimal to purchase one big fast drive. You can achieve
similar or even better results by using the ccd (concatenated
disk) driver to create a striped disk array out of multiple slower
drives for comparable overall cost.</para>
<para>Make sure you have adequate air flow around the drive,
especially if you are going to use a fast-spinning drive. You
generally need at least 1/2” (1.25cm) of spacing above and below a
drive. Understand how the air flows through your PC case. Most
cases have the power supply suck the air out of the back. See
where the air flows in, and put the drive where it will have the
largest volume of cool air flowing around it. You may need to seal
some unwanted holes or add a new fan for effective cooling.</para>
<para>Another consideration is noise. Many 10,000 or faster drives
generate a high-pitched whine which is quite unpleasant to most
people. That, plus the extra fans often required for cooling, may
make 10,000 or faster drives unsuitable for some office and home
environments.</para>
</sect3>
<sect3>
<title>Form factor</title>
<para>Most SCSI drives sold today are of 3.5” form factor. They
come in two different heights; 1.6” (<quote>half-height</quote>) or
1” (<quote>low-profile</quote>). The half-height drive is the same
height as a CDROM drive. However, do not forget the spacing rule
mentioned in the previous section. If you have three standard
3.5” drive bays, you will not be able to put three half-height
drives in there (without frying them, that is).</para>
</sect3>
<sect3>
<title>Interface</title>
<para>The majority of SCSI hard drives sold today are Ultra,
Ultra-wide, or Ultra160 SCSI. As of this writing (June 2002),
the first Ultra320 host adapters and devices become available.
The maximum bandwidth of Ultra SCSI is 20MB/sec,
and Ultra-wide SCSI is 40MB/sec. Ultra160 can transfer 160MB/sec
and Ultra320 can transfer 320MB/sec. There is no difference in max
cable length between Ultra and Ultra-wide; however, the more
devices you have on the same bus, the sooner you will start having
bus integrity problems. Unless you have a well-designed disk
enclosure, it is not easy to make more than 5 or 6 Ultra SCSI
drives work on a single bus.</para>
<para>On the other hand, if you need to connect many drives, going
for Fast-wide SCSI may not be a bad idea. That will have the same
max bandwidth as Ultra (narrow) SCSI, while electronically it is
much easier to get it <quote>right</quote>. My advice would be: if
you want to connect many disks, get wide or Ultra160 SCSI drives;
they usually
cost a little more but it may save you down the road. (Besides,
if you can not afford the cost difference, you should not be building
a disk array.)</para>
<para>There are two variant of wide SCSI drives; 68-pin and 80-pin
SCA (Single Connector Attach). The SCA drives do not have a
separate 4-pin power connector, and also read the SCSI ID settings
through the 80-pin connector. If you are really serious about
building a large storage system, get SCA drives and a good SCA
enclosure (dual power supply with at least one extra fan). They
are more electronically sound than 68-pin counterparts because
there is no <quote>stub</quote> of the SCSI bus inside the disk
canister as in arrays built from 68-pin drives. They are easier
to install too (you just need to screw the drive in the canister,
instead of trying to squeeze in your fingers in a tight place to
hook up all the little cables (like the SCSI ID and disk activity
LED lines).</para>
</sect3>
</sect2>
<sect2>
<title>* IDE hard drives</title>
<para></para>
</sect2>
</sect1>
<sect1>
<title>Tape drives</title>
<para><emphasis>Contributed by &a.jmb;. 2 July
1996.</emphasis></para>
<sect2>
<title>General tape access commands</title>
<para>&man.mt.1; provides generic access to the tape drives. Some of
the more common commands are <command>rewind</command>,
<command>erase</command>, and <command>status</command>. See the
&man.mt.1; manual page for a detailed description.</para>
</sect2>
<sect2>
<title>Controller Interfaces</title>
<para>There are several different interfaces that support tape drives.
The interfaces are SCSI, IDE, Floppy and Parallel Port. A wide
variety of tape drives are available for these interfaces.
Controllers are discussed in <link
linkend="hw-storage-controllers">Disk/tape
controllers</link>.</para>
</sect2>
<sect2>
<title>SCSI drives</title>
<para>The &man.st.4; driver provides support for 8mm (Exabyte), 4mm
(DAT: Digital Audio Tape), QIC (Quarter-Inch Cartridge), DLT
(Digital Linear Tape), QIC Mini cartridge and 9-track (remember the
big reels that you see spinning in Hollywood computer rooms) tape
drives. See the &man.st.4; manual page for a detailed
description.</para>
<para>The drives listed below are currently being used by members of
the FreeBSD community. They are not the only drives that will work
with FreeBSD. They just happen to be the ones that we use.</para>
<sect3>
<title>4mm (DAT: Digital Audio Tape)</title>
<para><link linkend="hw-storage-python-28454">Archive Python
28454</link></para>
<para><link linkend="hw-storage-python-04687">Archive Python
04687</link></para>
<para><link linkend="hw-storage-hp1533a">HP C1533A</link></para>
<para><link linkend="hw-storage-hp1534a">HP C1534A</link></para>
<para><link linkend="hw-storage-hp35450a">HP 35450A</link></para>
<para><link linkend="hw-storage-hp35470a">HP 35470A</link></para>
<para><link linkend="hw-storage-hp35480a">HP 35480A</link></para>
<para><link linkend="hw-storage-sdt5000">SDT-5000</link></para>
<para><link linkend="hw-storage-wangtek6200">Wangtek
6200</link></para>
</sect3>
<sect3>
<title>8mm (Exabyte)</title>
<para><link linkend="hw-storage-exb8200">EXB-8200</link></para>
<para><link linkend="hw-storage-exb8500">EXB-8500</link></para>
<para><link linkend="hw-storage-exb8505">EXB-8505</link></para>
</sect3>
<sect3>
<title>QIC (Quarter-Inch Cartridge)</title>
<para><link linkend="hw-storage-anaconda">Archive Anaconda
2750</link></para>
<para><link linkend="hw-storage-viper60">Archive Viper
60</link></para>
<para><link linkend="hw-storage-viper150">Archive Viper
150</link></para>
<para><link linkend="hw-storage-viper2525">Archive Viper
2525</link></para>
<para><link linkend="hw-storage-tandberg3600">Tandberg TDC
3600</link></para>
<para><link linkend="hw-storage-tandberg3620">Tandberg TDC
3620</link></para>
<para><link linkend="hw-storage-tandberg3800">Tandberg TDC
3800</link></para>
<para><link linkend="hw-storage-tandberg4222">Tandberg TDC
4222</link></para>
<para><link linkend="hw-storage-wangtek5525es">Wangtek
5525ES</link></para>
</sect3>
<sect3>
<title>DLT (Digital Linear Tape)</title>
<para><link linkend="hw-storage-dectz87">Digital TZ87</link></para>
</sect3>
<sect3>
<title>Mini-Cartridge</title>
<para><link linkend="hw-storage-ctms3200">Conner CTMS
3200</link></para>
<para><link linkend="hw-storage-exb2501">Exabyte 2501</link></para>
</sect3>
<sect3>
<title>Autoloaders/Changers</title>
<para><link linkend="hw-storage-hp1553a">Hewlett-Packard HP C1553A
Autoloading DDS2</link></para>
</sect3>
</sect2>
<sect2>
<title>* IDE drives</title>
<para></para>
</sect2>
<sect2>
<title>Floppy drives</title>
<para><link linkend="hw-storage-conner420r">Conner 420R</link></para>
</sect2>
<sect2>
<title>* Parallel port drives</title>
<para></para>
</sect2>
<sect2>
<title>Detailed Information</title>
<sect3 id="hw-storage-anaconda">
<title>Archive Anaconda 2750</title>
<para>The boot message identifier for this drive is <literal>ARCHIVE
ANCDA 2750 28077 -003 type 1 removable SCSI 2</literal></para>
<para>This is a QIC tape drive.</para>
<para>Native capacity is 1.35GB when using QIC-1350 tapes. This
drive will read and write QIC-150 (DC6150), QIC-250 (DC6250), and
QIC-525 (DC6525) tapes as well.</para>
<para>Data transfer rate is 350kB/s using &man.dump.8;.
Rates of 530kB/s have been reported when using
Amanda</para>
<para>Production of this drive has been discontinued.</para>
<para>The SCSI bus connector on this tape drive is reversed from
that on most other SCSI devices. Make sure that you have enough
SCSI cable to twist the cable one-half turn before and after the
Archive Anaconda tape drive, or turn your other SCSI devices
upside-down.</para>
<para>Two kernel code changes are required to use this drive. This
drive will not work as delivered.</para>
<para>If you have a SCSI-2 controller, short jumper 6. Otherwise,
the drive behaves are a SCSI-1 device. When operating as a SCSI-1
device, this drive, <quote>locks</quote> the SCSI bus during some
tape operations, including: fsf, rewind, and rewoffl.</para>
<para>If you are using the NCR SCSI controllers, patch the file
<filename>/usr/src/sys/pci/ncr.c</filename> (as shown below).
Build and install a new kernel.</para>
<programlisting>*** 4831,4835 ****
};
! if (np->latetime>4) {
/*
** Although we tried to wake it up,
--- 4831,4836 ----
};
! if (np->latetime>1200) {
/*
** Although we tried to wake it up,</programlisting>
<para>Reported by: &a.jmb;</para>
</sect3>
<sect3 id="hw-storage-python-28454">
<title>Archive Python 28454</title>
<para>The boot message identifier for this drive is <literal>ARCHIVE
Python 28454-XXX4ASB</literal> <literal>type 1 removable SCSI
2</literal> <literal>density code 0x8c, 512-byte
blocks</literal></para>
<para>This is a DDS-1 tape drive.</para>
<para>Native capacity is 2.5GB on 90m tapes.</para>
<para>Data transfer rate is XXX.</para>
<para>This drive was repackaged by Sun Microsystems as model
595-3067.</para>
<para>Reported by: Bob Bishop <email>rb@gid.co.uk</email></para>
<para>Throughput is in the 1.5 MByte/sec range, however this will
drop if the disks and tape drive are on the same SCSI
controller.</para>
<para>Reported by: Robert E. Seastrom
<email>rs@seastrom.com</email></para>
</sect3>
<sect3 id="hw-storage-python-04687">
<title>Archive Python 04687</title>
<para>The boot message identifier for this drive is <literal>ARCHIVE
Python 04687-XXX 6580</literal> <literal>Removable Sequential
Access SCSI-2 device</literal></para>
<para>This is a DAT-DDS-2 drive.</para>
<para>Native capacity is 4GB when using 120m tapes.</para>
<para>This drive supports hardware data compression. Switch 4
controls MRS (Media Recognition System). MRS tapes have stripes
on the transparent leader. Switch 4 <emphasis>off</emphasis>
enables MRS, <emphasis>on</emphasis> disables MRS.</para>
<para>Parity is controlled by switch 5. Switch 5
<emphasis>on</emphasis> to enable parity control. Compression is
enabled with Switch 6 <emphasis>off</emphasis>. It is possible to
override compression with the <literal>SCSI MODE SELECT</literal>
command (see &man.mt.1;).</para>
<para>Data transfer rate is 800kB/s.</para>
</sect3>
<sect3 id="hw-storage-viper60">
<title>Archive Viper 60</title>
<para>The boot message identifier for this drive is <literal>ARCHIVE
VIPER 60 21116 -007</literal> <literal>type 1 removable SCSI
1</literal></para>
<para>This is a QIC tape drive.</para>
<para>Native capacity is 60MB.</para>
<para>Data transfer rate is XXX.</para>
<para>Production of this drive has been discontinued.</para>
<para>Reported by: Philippe Regnauld
<email>regnauld@hsc.fr</email></para>
</sect3>
<sect3 id="hw-storage-viper150">
<title>Archive Viper 150</title>
<para>The boot message identifier for this drive is <literal>ARCHIVE
VIPER 150 21531 -004</literal> <literal>Archive Viper 150 is a
known rogue</literal> <literal>type 1 removable SCSI
1</literal>. A multitude of firmware revisions exist for this
drive. Your drive may report different numbers (e.g
<literal>21247 -005</literal>.</para>
<para>This is a QIC tape drive.</para>
<para>Native capacity is 150/250MB. Both 150MB (DC6150) and 250MB
(DC6250) tapes have the recording format. The 250MB tapes are
approximately 67% longer than the 150MB tapes. This drive can
read 120MB tapes as well. It can not write 120MB tapes.</para>
<para>Data transfer rate is 100kB/s</para>
<para>This drive reads and writes DC6150 (150MB) and DC6250 (250MB)
tapes.</para>
<para>This drives quirks are known and pre-compiled into the SCSI
tape device driver (&man.st.4;).</para>
<para>Under FreeBSD 2.2-CURRENT, use <command>mt blocksize
512</command> to set the blocksize. (The particular drive had
firmware revision 21247 -005. Other firmware revisions may behave
differently) Previous versions of FreeBSD did not have this
problem.</para>
<para>Production of this drive has been discontinued.</para>
<para>Reported by: Pedro A M Vazquez
<email>vazquez@IQM.Unicamp.BR</email></para>
<para>&a.msmith;</para>
</sect3>
<sect3 id="hw-storage-viper2525">
<title>Archive Viper 2525</title>
<para>The boot message identifier for this drive is <literal>ARCHIVE
VIPER 2525 25462 -011</literal> <literal>type 1 removable SCSI
1</literal></para>
<para>This is a QIC tape drive.</para>
<para>Native capacity is 525MB.</para>
<para>Data transfer rate is 180kB/s at 90 inches/sec.</para>
<para>The drive reads QIC-525, QIC-150, QIC-120 and QIC-24 tapes.
Writes QIC-525, QIC-150, and QIC-120.</para>
<para>Firmware revisions prior to <literal>25462 -011</literal> are
bug ridden and will not function properly.</para>
<para>Production of this drive has been discontinued.</para>
</sect3>
<sect3 id="hw-storage-conner420r">
<title>Conner 420R</title>
<para>The boot message identifier for this drive is <literal>Conner
tape</literal>.</para>
<para>This is a floppy controller, mini cartridge tape drive.</para>
<para>Native capacity is XXXX</para>
<para>Data transfer rate is XXX</para>
<para>The drive uses QIC-80 tape cartridges.</para>
<para>Reported by: Mark Hannon
<email>mark@seeware.DIALix.oz.au</email></para>
</sect3>
<sect3 id="hw-storage-ctms3200">
<title>Conner CTMS 3200</title>
<para>The boot message identifier for this drive is <literal>CONNER
CTMS 3200 7.00</literal> <literal>type 1 removable SCSI
2</literal>.</para>
<para>This is a mini cartridge tape drive.</para>
<para>Native capacity is XXXX</para>
<para>Data transfer rate is XXX</para>
<para>The drive uses QIC-3080 tape cartridges.</para>
<para>Reported by: Thomas S. Traylor
<email>tst@titan.cs.mci.com</email></para>
</sect3>
<sect3 id="hw-storage-dectz87">
<title><ulink
url="http://www.digital.com/info/Customer-Update/931206004.txt.html">DEC TZ87</ulink></title>
<para>The boot message identifier for this drive is <literal>DEC
TZ87 (C) DEC 9206</literal> <literal>type 1 removable SCSI
2</literal> <literal>density code 0x19</literal></para>
<para>This is a DLT tape drive.</para>
<para>Native capacity is 10GB.</para>
<para>This drive supports hardware data compression.</para>
<para>Data transfer rate is 1.2MB/s.</para>
<para>This drive is identical to the Quantum DLT2000. The drive
firmware can be set to emulate several well-known drives,
including an Exabyte 8mm drive.</para>
<para>Reported by: &a.wilko;</para>
</sect3>
<sect3 id="hw-storage-exb2501">
<title><ulink
url="http://www.Exabyte.COM:80/Products/Minicartridge/2501/Rfeatures.html">Exabyte EXB-2501</ulink></title>
<para>The boot message identifier for this drive is <literal>EXABYTE
EXB-2501</literal></para>
<para>This is a mini-cartridge tape drive.</para>
<para>Native capacity is 1GB when using MC3000XL
mini cartridges.</para>
<para>Data transfer rate is XXX</para>
<para>This drive can read and write DC2300 (550MB), DC2750 (750MB),
MC3000 (750MB), and MC3000XL (1GB) mini cartridges.</para>
<para>WARNING: This drive does not meet the SCSI-2 specifications.
The drive locks up completely in response to a SCSI MODE_SELECT
command unless there is a formatted tape in the drive. Before
using this drive, set the tape blocksize with</para>
<screen>&prompt.root; <userinput>mt -f /dev/st0ctl.0 blocksize 1024</userinput></screen>
<para>Before using a mini cartridge for the first time, the
mini cartridge must be formatted. FreeBSD 2.1.0-RELEASE and
earlier:</para>
<screen>&prompt.root; <userinput>/sbin/scsi -f /dev/rst0.ctl -s 600 -c "4 0 0 0 0 0"</userinput></screen>
<para>(Alternatively, fetch a copy of the
<command>scsiformat</command> shell script from FreeBSD
2.1.5/2.2.) FreeBSD 2.1.5 and later:</para>
<screen>&prompt.root; <userinput>/sbin/scsiformat -q -w /dev/rst0.ctl</userinput></screen>
<para>Right now, this drive cannot really be recommended for
FreeBSD.</para>
<para>Reported by: Bob Beaulieu
<email>ez@eztravel.com</email></para>
</sect3>
<sect3 id="hw-storage-exb8200">
<title>Exabyte EXB-8200</title>
<para>The boot message identifier for this drive is <literal>EXABYTE
EXB-8200 252X</literal> <literal>type 1 removable SCSI
1</literal></para>
<para>This is an 8mm tape drive.</para>
<para>Native capacity is 2.3GB.</para>
<para>Data transfer rate is 270kB/s.</para>
<para>This drive is fairly slow in responding to the SCSI bus during
boot. A custom kernel may be required (set SCSI_DELAY to 10
seconds).</para>
<para>There are a large number of firmware configurations for this
drive, some have been customized to a particular vendor's
hardware. The firmware can be changed via EPROM
replacement.</para>
<para>Production of this drive has been discontinued.</para>
<para>Reported by: &a.msmith;</para>
</sect3>
<sect3 id="hw-storage-exb8500">
<title>Exabyte EXB-8500</title>
<para>The boot message identifier for this drive is <literal>EXABYTE
EXB-8500-85Qanx0 0415</literal> <literal>type 1 removable SCSI
2</literal></para>
<para>This is an 8mm tape drive.</para>
<para>Native capacity is 5GB.</para>
<para>Data transfer rate is 300kB/s.</para>
<para>Reported by: Greg Lehey <email>grog@lemis.de</email></para>
</sect3>
<sect3 id="hw-storage-exb8505">
<title><ulink
url="http://www.Exabyte.COM:80/Products/8mm/8505XL/Rfeatures.html">Exabyte EXB-8505</ulink></title>
<para>The boot message identifier for this drive is
<literal>EXABYTE EXB-85058SQANXR1 05B0</literal> <literal>type 1
removable SCSI 2</literal></para>
<para>This is an 8mm tape drive which supports compression, and is
upward compatible with the EXB-5200 and EXB-8500.</para>
<para>Native capacity is 5GB.</para>
<para>The drive supports hardware data compression.</para>
<para>Data transfer rate is 300kB/s.</para>
<para>Reported by: Glen Foster
<email>gfoster@gfoster.com</email></para>
</sect3>
<sect3 id="hw-storage-hp1533a">
<title>Hewlett-Packard HP C1533A</title>
<para>The boot message identifier for this drive is <literal>HP
C1533A 9503</literal> <literal>type 1 removable SCSI
2</literal>.</para>
<para>This is a DDS-2 tape drive. DDS-2 means hardware data
compression and narrower tracks for increased data
capacity.</para>
<para>Native capacity is 4GB when using 120m tapes. This drive
supports hardware data compression.</para>
<para>Data transfer rate is 510kB/s.</para>
<para>This drive is used in Hewlett-Packard's SureStore 6000eU and
6000i tape drives and C1533A DDS-2 DAT drive.</para>
<para>The drive has a block of 8 dip switches. The proper settings
for FreeBSD are: 1 ON; 2 ON; 3 OFF; 4 ON; 5 ON; 6 ON; 7 ON; 8
ON.</para>
<informaltable frame="none" pgwide="1">
<tgroup cols="3">
<thead>
<row>
<entry>switch 1</entry>
<entry>switch 2</entry>
<entry>Result</entry>
</row>
</thead>
<tbody>
<row>
<entry>On</entry>
<entry>On</entry>
<entry>Compression enabled at power-on, with host
control</entry>
</row>
<row>
<entry>On</entry>
<entry>Off</entry>
<entry>Compression enabled at power-on, no host
control</entry>
</row>
<row>
<entry>Off</entry>
<entry>On</entry>
<entry>Compression disabled at power-on, with host
control</entry>
</row>
<row>
<entry>Off</entry>
<entry>Off</entry>
<entry>Compression disabled at power-on, no host
control</entry>
</row>
</tbody>
</tgroup>
</informaltable>
<para>Switch 3 controls MRS (Media Recognition System). MRS tapes
have stripes on the transparent leader. These identify the tape
as DDS (Digital Data Storage) grade media. Tapes that do not have
the stripes will be treated as write-protected. Switch 3 OFF
enables MRS. Switch 3 ON disables MRS.</para>
<para>See <ulink url="http://www.hp.com/tape/c_intro.html">HP
SureStore Tape Products</ulink> and <ulink
url="http://www.impediment.com/hp/hp_technical.html">Hewlett-Packard
Disk and Tape Technical Information</ulink> for more information
on configuring this drive.</para>
<para><emphasis>Warning:</emphasis> Quality control on these drives
varies greatly. One FreeBSD core-team member has returned 2 of
these drives. Neither lasted more than 5 months.</para>
<para>Reported by: &a.se;</para>
</sect3>
<sect3 id="hw-storage-hp1534a">
<title>Hewlett-Packard HP 1534A</title>
<para>The boot message identifier for this drive is <literal>HP
HP35470A T503</literal> <literal>type 1 removable SCSI
2</literal> <literal>Sequential-Access density code 0x13,
variable blocks</literal>.</para>
<para>This is a DDS-1 tape drive. DDS-1 is the original DAT tape
format.</para>
<para>Native capacity is 2GB when using 90m tapes.</para>
<para>Data transfer rate is 183kB/s.</para>
<para>The same mechanism is used in Hewlett-Packard's SureStore
<ulink url="http://www.dmo.hp.com/tape/sst2000.htm">2000i</ulink>
tape drive, C35470A DDS format DAT drive, C1534A DDS format DAT
drive and HP C1536A DDS format DAT drive.</para>
<para>The HP C1534A DDS format DAT drive has two indicator lights,
one green and one amber. The green one indicates tape action:
slow flash during load, steady when loaded, fast flash during
read/write operations. The amber one indicates warnings: slow
flash when cleaning is required or tape is nearing the end of its
useful life, steady indicates an hard fault. (factory service
required?)</para>
<para>Reported by Gary Crutcher
<email>gcrutchr@nightflight.com</email></para>
</sect3>
<sect3 id="hw-storage-hp1553a">
<title>Hewlett-Packard HP C1553A Autoloading DDS2</title>
<para>The boot message identifier for this drive is "".</para>
<para>This is a DDS-2 tape drive with a tape changer. DDS-2 means
hardware data compression and narrower tracks for increased data
capacity.</para>
<para>Native capacity is 24GB when using 120m tapes. This drive
supports hardware data compression.</para>
<para>Data transfer rate is 510kB/s (native).</para>
<para>This drive is used in Hewlett-Packard's SureStore <ulink
url="http://www.dmo.hp.com/tape/sst12000.htm">12000e</ulink>
tape drive.</para>
<para>The drive has two selectors on the rear panel. The selector
closer to the fan is SCSI id. The other selector should be set to
7.</para>
<para>There are four internal switches. These should be set: 1 ON;
2 ON; 3 ON; 4 OFF.</para>
<para>At present the kernel drivers do not automatically change
tapes at the end of a volume. This shell script can be used to
change tapes:</para>
<programlisting>#!/bin/sh
PATH="/sbin:/usr/sbin:/bin:/usr/bin"; export PATH
usage()
{
echo "Usage: dds_changer [123456ne] raw-device-name
echo "1..6 = Select cartridge"
echo "next cartridge"
echo "eject magazine"
exit 2
}
if [ $# -ne 2 ] ; then
usage
fi
cdb3=0
cdb4=0
cdb5=0
case $1 in
[123456])
cdb3=$1
cdb4=1
;;
n)
;;
e)
cdb5=0x80
;;
?)
usage
;;
esac
scsi -f $2 -s 100 -c "1b 0 0 $cdb3 $cdb4 $cdb5"</programlisting>
</sect3>
<sect3 id="hw-storage-hp35450a">
<title>Hewlett-Packard HP 35450A</title>
<para>The boot message identifier for this drive is <literal>HP
HP35450A -A C620</literal> <literal>type 1 removable SCSI
2</literal> <literal>Sequential-Access density code
0x13</literal></para>
<para>This is a DDS-1 tape drive. DDS-1 is the original DAT tape
format.</para>
<para>Native capacity is 1.2GB.</para>
<para>Data transfer rate is 160kB/s.</para>
<para>Reported by: Mark Thompson
<email>mark.a.thompson@pobox.com</email></para>
</sect3>
<sect3 id="hw-storage-hp35470a">
<title>Hewlett-Packard HP 35470A</title>
<para>The boot message identifier for this drive is <literal>HP
HP35470A 9 09</literal> <literal>type 1 removable SCSI
2</literal></para>
<para>This is a DDS-1 tape drive. DDS-1 is the original DAT tape
format.</para>
<para>Native capacity is 2GB when using 90m tapes.</para>
<para>Data transfer rate is 183kB/s.</para>
<para>The same mechanism is used in Hewlett-Packard's SureStore
<ulink url="http://www.dmo.hp.com/tape/sst2000.htm">2000i</ulink>
tape drive, C35470A DDS format DAT drive, C1534A DDS format DAT
drive, and HP C1536A DDS format DAT drive.</para>
<para><emphasis>Warning:</emphasis> Quality control on these drives
varies greatly. One FreeBSD core-team member has returned 5 of
these drives. None lasted more than 9 months.</para>
<para>Reported by: David Dawes
<email>dawes@rf900.physics.usyd.edu.au</email> (9 09)</para>
</sect3>
<sect3 id="hw-storage-hp35480a">
<title>Hewlett-Packard HP 35480A</title>
<para>The boot message identifier for this drive is <literal>HP
HP35480A 1009</literal> <literal>type 1 removable SCSI
2</literal> <literal>Sequential-Access density code
0x13</literal>.</para>
<para>This is a DDS-DC tape drive. DDS-DC is DDS-1 with hardware
data compression. DDS-1 is the original DAT tape format.</para>
<para>Native capacity is 2GB when using 90m tapes. It cannot handle
120m tapes. This drive supports hardware data compression.
Please refer to the section on <link
linkend="hw-storage-hp1533a">HP C1533A</link> for the proper
switch settings.</para>
<para>Data transfer rate is 183kB/s.</para>
<para>This drive is used in Hewlett-Packard's SureStore <ulink
url="http://www.dmo.hp.com/tape/sst5000.htm">5000eU</ulink> and
<ulink url="http://www.dmo.hp.com/tape/sst5000.htm">5000i</ulink>
tape drives and C35480A DDS format DAT drive..</para>
<para>This drive will occasionally hang during a tape eject
operation (<command>mt offline</command>). Pressing the front
panel button will eject the tape and bring the tape drive back to
life.</para>
<para>WARNING: HP 35480-03110 only. On at least two occasions this
tape drive when used with FreeBSD 2.1.0, an IBM Server 320 and an
2940W SCSI controller resulted in all SCSI disk partitions being
lost. The problem has not be analyzed or resolved at this
time.</para>
</sect3>
<sect3 id="hw-storage-sdt5000">
<title><ulink
url="http://www.sel.sony.com/SEL/ccpg/storage/tape/t5000.html">Sony SDT-5000</ulink></title>
<para>There are at least two significantly different models: one is
a DDS-1 and the other DDS-2. The DDS-1 version is
<literal>SDT-5000 3.02</literal>. The DDS-2 version is
<literal>SONY SDT-5000 327M</literal>. The DDS-2 version has a 1MB
cache. This cache is able to keep the tape streaming in almost
any circumstances.</para>
<para>The boot message identifier for this drive is <literal>SONY
SDT-5000 3.02</literal> <literal>type 1 removable SCSI
2</literal> <literal>Sequential-Access density code
0x13</literal></para>
<para>Native capacity is 4GB when using 120m tapes. This drive
supports hardware data compression.</para>
<para>Data transfer rate is depends upon the model or the drive. The
rate is 630kB/s for the <literal>SONY SDT-5000 327M</literal>
while compressing the data. For the <literal>SONY SDT-5000
3.02</literal>, the data transfer rate is 225kB/s.</para>
<para>In order to get this drive to stream, set the blocksize to 512
bytes (<command>mt blocksize 512</command>) reported by Kenneth
Merry <email>ken@ulc199.residence.gatech.edu</email>.</para>
<para><literal>SONY SDT-5000 327M</literal> information reported by
Charles Henrich <email>henrich@msu.edu</email>.</para>
<para>Reported by: &a.jmz;</para>
</sect3>
<sect3 id="hw-storage-tandberg3600">
<title>Tandberg TDC 3600</title>
<para>The boot message identifier for this drive is
<literal>TANDBERG TDC 3600 =08:</literal> <literal>type 1
removable SCSI 2</literal></para>
<para>This is a QIC tape drive.</para>
<para>Native capacity is 150/250MB.</para>
<para>This drive has quirks which are known and work around code is
present in the SCSI tape device driver (&man.st.4;).
Upgrading the firmware to XXX version will fix the quirks and
provide SCSI 2 capabilities.</para>
<para>Data transfer rate is 80kB/s.</para>
<para>IBM and Emerald units will not work. Replacing the firmware
EPROM of these units will solve the problem.</para>
<para>Reported by: &a.msmith;</para>
</sect3>
<sect3 id="hw-storage-tandberg3620">
<title>Tandberg TDC 3620</title>
<para>This is very similar to the <link
linkend="hw-storage-tandberg3600">Tandberg TDC 3600</link>
drive.</para>
<para>Reported by: &a.joerg;</para>
</sect3>
<sect3 id="hw-storage-tandberg3800">
<title>Tandberg TDC 3800</title>
<para>The boot message identifier for this drive is
<literal>TANDBERG TDC 3800 =04Y</literal> <literal>Removable
Sequential Access SCSI-2 device</literal></para>
<para>This is a QIC tape drive.</para>
<para>Native capacity is 525MB.</para>
<para>Reported by: &a.jhs;</para>
</sect3>
<sect3 id="hw-storage-tandberg4222">
<title>Tandberg TDC 4222</title>
<para>The boot message identifier for this drive is
<literal>TANDBERG TDC 4222 =07</literal> <literal>type 1 removable
SCSI 2</literal></para>
<para>This is a QIC tape drive.</para>
<para>Native capacity is 2.5GB. The drive will read all cartridges
from the 60 MB (DC600A) upwards, and write 150 MB (DC6150)
upwards. Hardware compression is optionally supported for the 2.5
GB cartridges.</para>
<para>This drives quirks are known and pre-compiled into the SCSI
tape device driver (&man.st.4;) beginning with FreeBSD
2.2-CURRENT. For previous versions of FreeBSD, use
<command>mt</command> to read one block from the tape, rewind the
tape, and then execute the backup program (<command>mt fsr 1; mt
rewind; dump ...</command>)</para>
<para>Data transfer rate is 600kB/s (vendor claim with compression),
350 KB/s can even be reached in start/stop mode. The rate
decreases for smaller cartridges.</para>
<para>Reported by: &a.joerg;</para>
</sect3>
<sect3 id="hw-storage-wangtek5525es">
<title>Wangtek 5525ES</title>
<para>The boot message identifier for this drive is <literal>WANGTEK
5525ES SCSI REV7 3R1</literal> <literal>type 1 removable SCSI
1</literal> <literal>density code 0x11, 1024-byte
blocks</literal></para>
<para>This is a QIC tape drive.</para>
<para>Native capacity is 525MB.</para>
<para>Data transfer rate is 180kB/s.</para>
<para>The drive reads 60, 120, 150, and 525MB tapes. The drive will
not write 60MB (DC600 cartridge) tapes. In order to overwrite 120
and 150 tapes reliably, first erase (<command>mt erase</command>)
the tape. 120 and 150 tapes used a wider track (fewer tracks per
tape) than 525MB tapes. The <quote>extra</quote> width of the
previous tracks is not overwritten, as a result the new data lies
in a band surrounded on both sides by the previous data unless the
tape have been erased.</para>
<para>This drives quirks are known and pre-compiled into the SCSI
tape device driver (&man.st.4;).</para>
<para>Other firmware revisions that are known to work are:
M75D</para>
<para>Reported by: Marc van Kempen <email>marc@bowtie.nl</email>
<literal>REV73R1</literal> Andrew Gordon
<email>Andrew.Gordon@net-tel.co.uk</email>
<literal>M75D</literal></para>
</sect3>
<sect3 id="hw-storage-wangtek6200">
<title>Wangtek 6200</title>
<para>The boot message identifier for this drive is <literal>WANGTEK
6200-HS 4B18</literal> <literal>type 1 removable SCSI
2</literal> <literal>Sequential-Access density code
0x13</literal></para>
<para>This is a DDS-1 tape drive.</para>
<para>Native capacity is 2GB using 90m tapes.</para>
<para>Data transfer rate is 150kB/s.</para>
<para>Reported by: Tony Kimball <email>alk@Think.COM</email></para>
</sect3>
</sect2>
<sect2>
<title>* Problem drives</title>
<para></para>
</sect2>
</sect1>
<sect1>
<title>CDROM drives</title>
<para><emphasis>Contributed by &a.obrien;. 23 November
1997.</emphasis></para>
<para>Generally speaking those in <emphasis>The FreeBSD
Project</emphasis> prefer SCSI CDROM drives over IDE CDROM
drives. However not all SCSI CDROM drives are equal. Some
feel the quality of some SCSI CDROM drives have been
deteriorating to that of IDE CDROM drives. Toshiba used to be
the favored stand-by, but many on the SCSI mailing list have
found displeasure with the 12x speed XM-5701TA as its volume
(when playing audio CDROMs) is not controllable by the various
audio player software.</para>
<para>Another area where SCSI CDROM manufacturers are cutting corners is
adherence to the <link linkend="scsi-further-reading">SCSI
specification</link>. Many SCSI CDROMs will respond to <link
linkend="scsi-rogue-devices">multiple LUNs</link> for its target
address. Known violators include the 6x Teac CD-56S 1.0D.</para>
</sect1>
</article>
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