1.\" Copyright (c) 1996 2.\" Julian Elischer <julian@freebsd.org>. All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 10.\" 2. Redistributions in binary form must reproduce the above copyright 11.\" notice, this list of conditions and the following disclaimer in the 12.\" documentation and/or other materials provided with the distribution. 13.\" 14.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 15.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 16.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 17.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 18.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 19.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 20.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 21.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 22.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 23.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 24.\" SUCH DAMAGE. 25.\" 26.\" $Id: st.4,v 1.11 1997/03/07 02:49:34 jmg Exp $ 27.\" 28.Dd October 15, 1998 29.Dt SA 4 30.Os FreeBSD 31.Sh NAME 32.Nm sa 33.Nd SCSI Sequential Access Device Driver 34.Sh SYNOPSIS 35.Cd device sa0 36.Cd device sa1 at scbus0 target 4 lun 0 37.Sh DESCRIPTION 38The 39.Nm sa 40driver provides support for all 41.Tn SCSI 42devices of the sequential access class that are attached to the system 43through a supported 44.Tn SCSI 45Host Adapter. 46The sequential access class includes tape and other linear access devices. 47.Pp 48A 49.Tn SCSI 50Host 51adapter must also be separately configured into the system 52before a 53.Tn SCSI 54sequential access device can be configured. 55.Sh MOUNT SESSIONS 56The 57.Nm 58driver is based around the concept of a 59.Dq Em mount session , 60which is defined as the period between the time that a tape is 61mounted, and the time when it is unmounted. Any parameters set during 62a mount session remain in effect for the remainder of the session or 63until replaced. The tape can be unmounted, bringing the session to a 64close in several ways. These include: 65.Bl -enum 66.It 67Closing a `rewind device', 68referred to as sub-mode 00 below. An example is 69.Pa /dev/rsa0 . 70.It 71Using the MTOFFL 72.Xr ioctl 2 73command, reachable through the 74.Sq Cm offline 75command of 76.Xr mt 1 . 77.Sh SUB-MODES 78Bits 0 and 1 of the minor number are interpreted as 79.Sq sub-modes . 80The sub-modes differ in the action taken when the device is closed: 81.Bl -tag -width XXXX 82.It 00 83A close will rewind the device; if the tape has been 84written, then a file mark will be written before the rewind is requested. 85The device is unmounted. 86.It 01 87A close will leave the tape mounted. 88If the tape was written to, a file mark will be written. 89No other head positioning takes place. 90Any further reads or writes will occur directly after the 91last read, or the written file mark. 92.It 10 93A close will rewind the device. If the tape has been 94written, then a file mark will be written before the rewind is requested. 95On completion of the rewind an unload command will be issued. 96The device is unmounted. 97.Sh BLOCKING MODES 98.Tn SCSI 99tapes may run in either 100.Sq Em variable 101or 102.Sq Em fixed 103block-size modes. Most 104.Tn QIC Ns -type 105devices run in fixed block-size mode, where most nine-track tapes and 106many new cartridge formats allow variable block-size. The difference 107between the two is as follows: 108.Bl -inset 109.It Variable block-size: 110Each write made to the device results in a single logical record 111written to the tape. One can never read or write 112.Em part 113of a record from tape (though you may request a larger block and read 114a smaller record); nor can one read multiple blocks. Data from a 115single write is therefore read by a single read. The block size used 116may be any value supported by the device, the 117.Tn SCSI 118adapter and the system (usually between 1 byte and 64 Kbytes, 119sometimes more). 120.Pp 121When reading a variable record/block from the tape, the head is 122logically considered to be immediately after the last item read, 123and before the next item after that. If the next item is a file mark, 124but it was never read, then the next 125process to read will immediately hit the file mark and receive an end-of-file notification. 126.It Fixed block-size 127Data written by the user is passed to the tape as a succession of 128fixed size blocks. It may be contiguous in memory, but it is 129considered to be a series of independent blocks. One may never write 130an amount of data that is not an exact multiple of the blocksize. One 131may read and write the same data as a different set of records, In 132other words, blocks that were written together may be read separately, 133and vice-versa. 134.Pp 135If one requests more blocks than remain in the file, the drive will 136encounter the file mark. Because there is some data to return (unless 137there were no records before the file mark), the read will succeed, 138returning that data, The next read will return immediately with a value 139of 0. (As above, if the file mark is never read, it remains for the next 140process to read if in no-rewind mode.) 141.El 142.Sh FILE MARK HANDLING 143The handling of file marks on write is automatic. If the user has 144written to the tape, and has not done a read since the last write, 145then a file mark will be written to the tape when the device is 146closed. If a rewind is requested after a write, then the driver 147assumes that the last file on the tape has been written, and ensures 148that there are two file marks written to the tape. The exception to 149this is that there seems to be a standard (which we follow, but don't 150understand why) that certain types of tape do not actually write two 151file marks to tape, but when read, report a `phantom' file mark when the 152last file is read. These devices include the QIC family of devices. 153(It might be that this set of devices is the same set as that of fixed 154block devices. This has not been determined yet, and they are treated 155as separate behaviors by the driver at this time.) 156.Sh IOCTLS 157The 158.Nm sa 159driver supports all of the ioctls of 160.Xr mtio 4 . 161.Sh FILES 162.Bl -tag -width /dev/[n][e]rsa[0-9] -compact 163.It Pa /dev/[n][e]rsa[0-9] 164general form: 165.It Pa /dev/rsa0 166Rewind on close 167.It Pa /dev/nrsa0 168No rewind on close 169.It Pa /dev/erst0 170Eject on close (if capable) 171.Sh BUGS 172This driver lacks many of the hacks required to deal with older devices. 173Many older 174.Tn SCSI-1 175devices may not work properly with this driver yet. 176.Pp 177The device node interface for different tape formats and modes should 178be rethought after considering the strategies employed by other vendors. 179.Pp 180Support for fast indexing and tape status reporting is lacking. 181.Sh DIAGNOSTICS 182None. 183.Sh SEE ALSO 184.Xr mt 1 , 185.Xr scsi 4 , 186.Xr sa 9 187.Sh HISTORY 188The 189.Nm sa 190driver was written for the 191.Tn CAM 192.Tn SCSI 193subsystem by Justin T. Gibbs and Kenneth Merry. 194Many ideas were gleaned from the 195.Nm st 196device driver written and ported from 197.Tn Mach 1982.5 199by Julian Elischer. 200