190831dd81
st(4) man page. Take out most of the sd(4) and st(4) man pages and point to the new da(4) and sa(4) man pages. Add sa.4 to the makefile. Reviewed by: ken Submitted by: gibbs
200 lines
7.1 KiB
Groff
200 lines
7.1 KiB
Groff
.\" Copyright (c) 1996
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.\" Julian Elischer <julian@freebsd.org>. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\"
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $Id: st.4,v 1.11 1997/03/07 02:49:34 jmg Exp $
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.\"
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.Dd October 15, 1998
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.Dt SA 4
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.Os FreeBSD
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.Sh NAME
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.Nm sa
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.Nd SCSI Sequential Access Device Driver
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.Sh SYNOPSIS
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.Cd device sa0
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.Cd device sa1 at scbus0 target 4 lun 0
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.Sh DESCRIPTION
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The
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.Nm sa
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driver provides support for all
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.Tn SCSI
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devices of the sequential access class that are attached to the system
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through a supported
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.Tn SCSI
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Host Adapter.
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The sequential access class includes tape and other linear access devices.
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.Pp
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A
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.Tn SCSI
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Host
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adapter must also be separately configured into the system
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before a
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.Tn SCSI
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sequential access device can be configured.
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.Sh MOUNT SESSIONS
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The
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.Nm
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driver is based around the concept of a
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.Dq Em mount session ,
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which is defined as the period between the time that a tape is
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mounted, and the time when it is unmounted. Any parameters set during
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a mount session remain in effect for the remainder of the session or
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until replaced. The tape can be unmounted, bringing the session to a
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close in several ways. These include:
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.Bl -enum
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.It
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Closing a `rewind device',
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referred to as sub-mode 00 below. An example is
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.Pa /dev/rsa0 .
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.It
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Using the MTOFFL
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.Xr ioctl 2
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command, reachable through the
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.Sq Cm offline
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command of
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.Xr mt 1 .
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.Sh SUB-MODES
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Bits 0 and 1 of the minor number are interpreted as
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.Sq sub-modes .
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The sub-modes differ in the action taken when the device is closed:
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.Bl -tag -width XXXX
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.It 00
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A close will rewind the device; if the tape has been
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written, then a file mark will be written before the rewind is requested.
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The device is unmounted.
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.It 01
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A close will leave the tape mounted.
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If the tape was written to, a file mark will be written.
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No other head positioning takes place.
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Any further reads or writes will occur directly after the
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last read, or the written file mark.
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.It 10
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A close will rewind the device. If the tape has been
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written, then a file mark will be written before the rewind is requested.
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On completion of the rewind an unload command will be issued.
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The device is unmounted.
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.Sh BLOCKING MODES
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.Tn SCSI
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tapes may run in either
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.Sq Em variable
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or
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.Sq Em fixed
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block-size modes. Most
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.Tn QIC Ns -type
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devices run in fixed block-size mode, where most nine-track tapes and
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many new cartridge formats allow variable block-size. The difference
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between the two is as follows:
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.Bl -inset
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.It Variable block-size:
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Each write made to the device results in a single logical record
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written to the tape. One can never read or write
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.Em part
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of a record from tape (though you may request a larger block and read
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a smaller record); nor can one read multiple blocks. Data from a
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single write is therefore read by a single read. The block size used
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may be any value supported by the device, the
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.Tn SCSI
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adapter and the system (usually between 1 byte and 64 Kbytes,
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sometimes more).
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.Pp
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When reading a variable record/block from the tape, the head is
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logically considered to be immediately after the last item read,
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and before the next item after that. If the next item is a file mark,
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but it was never read, then the next
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process to read will immediately hit the file mark and receive an end-of-file notification.
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.It Fixed block-size
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Data written by the user is passed to the tape as a succession of
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fixed size blocks. It may be contiguous in memory, but it is
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considered to be a series of independent blocks. One may never write
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an amount of data that is not an exact multiple of the blocksize. One
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may read and write the same data as a different set of records, In
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other words, blocks that were written together may be read separately,
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and vice-versa.
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.Pp
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If one requests more blocks than remain in the file, the drive will
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encounter the file mark. Because there is some data to return (unless
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there were no records before the file mark), the read will succeed,
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returning that data, The next read will return immediately with a value
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of 0. (As above, if the file mark is never read, it remains for the next
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process to read if in no-rewind mode.)
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.El
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.Sh FILE MARK HANDLING
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The handling of file marks on write is automatic. If the user has
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written to the tape, and has not done a read since the last write,
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then a file mark will be written to the tape when the device is
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closed. If a rewind is requested after a write, then the driver
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assumes that the last file on the tape has been written, and ensures
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that there are two file marks written to the tape. The exception to
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this is that there seems to be a standard (which we follow, but don't
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understand why) that certain types of tape do not actually write two
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file marks to tape, but when read, report a `phantom' file mark when the
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last file is read. These devices include the QIC family of devices.
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(It might be that this set of devices is the same set as that of fixed
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block devices. This has not been determined yet, and they are treated
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as separate behaviors by the driver at this time.)
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.Sh IOCTLS
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The
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.Nm sa
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driver supports all of the ioctls of
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.Xr mtio 4 .
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.Sh FILES
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.Bl -tag -width /dev/[n][e]rsa[0-9] -compact
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.It Pa /dev/[n][e]rsa[0-9]
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general form:
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.It Pa /dev/rsa0
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Rewind on close
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.It Pa /dev/nrsa0
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No rewind on close
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.It Pa /dev/erst0
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Eject on close (if capable)
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.Sh BUGS
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This driver lacks many of the hacks required to deal with older devices.
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Many older
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.Tn SCSI-1
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devices may not work properly with this driver yet.
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.Pp
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The device node interface for different tape formats and modes should
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be rethought after considering the strategies employed by other vendors.
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.Pp
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Support for fast indexing and tape status reporting is lacking.
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.Sh DIAGNOSTICS
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None.
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.Sh SEE ALSO
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.Xr mt 1 ,
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.Xr scsi 4 ,
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.Xr sa 9
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.Sh HISTORY
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The
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.Nm sa
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driver was written for the
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.Tn CAM
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.Tn SCSI
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subsystem by Justin T. Gibbs and Kenneth Merry.
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Many ideas were gleaned from the
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.Nm st
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device driver written and ported from
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.Tn Mach
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2.5
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by Julian Elischer.
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