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.\" $FreeBSD: src/share/man/man4/sa.4,v 1.22.2.7 2001/08/17 13:08:39 ru Exp $ 27.\" $DragonFly: src/share/man/man4/sa.4,v 1.2 2003/06/17 04:36:59 dillon Exp $ 28.\" 29.Dd June 6, 1999 30.Dt SA 4 31.Os 32.Sh NAME 33.Nm sa 34.Nd SCSI Sequential Access device driver 35.Sh SYNOPSIS 36.Cd device sa 37.Cd device sa1 at scbus0 target 4 unit 0 38.Sh DESCRIPTION 39The 40.Nm 41driver provides support for all 42.Tn SCSI 43devices of the sequential access class that are attached to the system 44through a supported 45.Tn SCSI 46Host Adapter. 47The sequential access class includes tape and other linear access devices. 48.Pp 49A 50.Tn SCSI 51Host 52adapter must also be separately configured into the system 53before a 54.Tn SCSI 55sequential access device can be configured. 56.Sh MOUNT SESSIONS 57The 58.Nm 59driver is based around the concept of a 60.Dq Em mount session , 61which is defined as the period between the time that a tape is 62mounted, and the time when it is unmounted. Any parameters set during 63a mount session remain in effect for the remainder of the session or 64until replaced. 65The tape can be unmounted, bringing the session to a 66close in several ways. These include: 67.Bl -enum 68.It 69Closing a `rewind device', 70referred to as sub-mode 00 below. 71An example is 72.Pa /dev/sa0 . 73.It 74Using the MTOFFL 75.Xr ioctl 2 76command, reachable through the 77.Sq Cm offline 78command of 79.Xr mt 1 . 80.El 81.Pp 82It should be noted that tape devices are exclusive open devices, except in 83the case where a control mode device is opened. 84In the latter case, exclusive 85access is only sought when needed (e.g., to set parameters). 86.Sh SUB-MODES 87Bits 0 and 1 of the minor number are interpreted as 88.Sq sub-modes . 89The sub-modes differ in the action taken when the device is closed: 90.Bl -tag -width XXXX 91.It 00 92A close will rewind the device; if the tape has been 93written, then a file mark will be written before the rewind is requested. 94The device is unmounted. 95.It 01 96A close will leave the tape mounted. 97If the tape was written to, a file mark will be written. 98No other head positioning takes place. 99Any further reads or writes will occur directly after the 100last read, or the written file mark. 101.It 10 102A close will rewind the device. 103If the tape has been 104written, then a file mark will be written before the rewind is requested. 105On completion of the rewind an unload command will be issued. 106The device is unmounted. 107.El 108.Sh BLOCKING MODES 109.Tn SCSI 110tapes may run in either 111.Sq Em variable 112or 113.Sq Em fixed 114block-size modes. Most 115.Tn QIC Ns -type 116devices run in fixed block-size mode, where most nine-track tapes and 117many new cartridge formats allow variable block-size. The difference 118between the two is as follows: 119.Bl -inset 120.It Variable block-size: 121Each write made to the device results in a single logical record 122written to the tape. One can never read or write 123.Em part 124of a record from tape (though you may request a larger block and read 125a smaller record); nor can one read multiple blocks. Data from a 126single write is therefore read by a single read. 127The block size used 128may be any value supported by the device, the 129.Tn SCSI 130adapter and the system (usually between 1 byte and 64 Kbytes, 131sometimes more). 132.Pp 133When reading a variable record/block from the tape, the head is 134logically considered to be immediately after the last item read, 135and before the next item after that. 136If the next item is a file mark, 137but it was never read, then the next 138process to read will immediately hit the file mark and receive an end-of-file notification. 139.It Fixed block-size: 140Data written by the user is passed to the tape as a succession of 141fixed size blocks. It may be contiguous in memory, but it is 142considered to be a series of independent blocks. 143One may never write 144an amount of data that is not an exact multiple of the blocksize. One 145may read and write the same data as a different set of records, In 146other words, blocks that were written together may be read separately, 147and vice-versa. 148.Pp 149If one requests more blocks than remain in the file, the drive will 150encounter the file mark. Because there is some data to return (unless 151there were no records before the file mark), the read will succeed, 152returning that data, The next read will return immediately with a value 153of 0. (As above, if the file mark is never read, it remains for the next 154process to read if in no-rewind mode.) 155.El 156.Sh FILE MARK HANDLING 157The handling of file marks on write is automatic. 158If the user has 159written to the tape, and has not done a read since the last write, 160then a file mark will be written to the tape when the device is 161closed. If a rewind is requested after a write, then the driver 162assumes that the last file on the tape has been written, and ensures 163that there are two file marks written to the tape. The exception to 164this is that there seems to be a standard (which we follow, but don't 165understand why) that certain types of tape do not actually write two 166file marks to tape, but when read, report a `phantom' file mark when the 167last file is read. These devices include the QIC family of devices. 168(It might be that this set of devices is the same set as that of fixed 169block devices. This has not been determined yet, and they are treated 170as separate behaviors by the driver at this time.) 171.Sh IOCTLS 172The 173.Nm 174driver supports all of the ioctls of 175.Xr mtio 4 . 176.Sh FILES 177.Bl -tag -width /dev/[n][e]sa[0-9] -compact 178.It Pa /dev/[n][e]sa[0-9] 179general form: 180.It Pa /dev/sa0 181Rewind on close 182.It Pa /dev/nsa0 183No rewind on close 184.It Pa /dev/esa0 185Eject on close (if capable) 186.It Pa /dev/sa0.ctl 187Control mode device (to examine state while another program is 188accessing the device, e.g.). 189.El 190.Sh BUGS 191This driver lacks many of the hacks required to deal with older devices. 192Many older 193.Tn SCSI-1 194devices may not work properly with this driver yet. 195.Pp 196Additionally, certain 197tapes (QIC tapes mostly) that were written under 198.Fx 1992.X 200aren't automatically read correctly with this driver: you may need to 201explicitly set variable block mode or set to the blocksize that works best 202for your device in order to read tapes written under 203.Fx 2042.X. 205.Pp 206Fine grained density and compression mode support that is bound to specific 207device names needs to be added. 208.Pp 209Support for fast indexing by use of partitions is missing. 210.Sh DIAGNOSTICS 211None. 212.Sh SEE ALSO 213.Xr mt 1 , 214.Xr scsi 4 215.Sh HISTORY 216The 217.Nm 218driver was written for the 219.Tn CAM 220.Tn SCSI 221subsystem by Justin T. Gibbs and Kenneth Merry. 222Many ideas were gleaned from the 223.Nm st 224device driver written and ported from 225.Tn Mach 2262.5 227by 228.An Julian Elischer . 229.Pp 230The current owner of record is 231.An Matthew Jacob 232who has suffered too many 233years of breaking tape drivers. 234