2 .\" Julian Elischer <julian@FreeBSD.org>. All rights reserved.
4 .\" Redistribution and use in source and binary forms, with or without
5 .\" modification, are permitted provided that the following conditions
7 .\" 1. Redistributions of source code must retain the above copyright
8 .\" notice, this list of conditions and the following disclaimer.
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.
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
33 .Nd SCSI Sequential Access device driver
39 driver provides support for all
41 devices of the sequential access class that are attached to the system
45 The sequential access class includes tape and other linear access devices.
50 adapter must also be separately configured into the system
53 sequential access device can be configured.
57 driver is based around the concept of a
58 .Dq Em mount session ,
59 which is defined as the period between the time that a tape is
60 mounted, and the time when it is unmounted.
61 Any parameters set during
62 a mount session remain in effect for the remainder of the session or
64 The tape can be unmounted, bringing the session to a
65 close in several ways.
69 Closing a `rewind device',
70 referred to as sub-mode 00 below.
76 command, reachable through the
82 It should be noted that tape devices are exclusive open devices, except in
83 the case where a control mode device is opened.
84 In the latter case, exclusive
85 access is only sought when needed (e.g., to set parameters).
87 Bits 0 and 1 of the minor number are interpreted as
89 The sub-modes differ in the action taken when the device is closed:
92 A close will rewind the device; if the tape has been
93 written, then a file mark will be written before the rewind is requested.
94 The device is unmounted.
96 A close will leave the tape mounted.
97 If the tape was written to, a file mark will be written.
98 No other head positioning takes place.
99 Any further reads or writes will occur directly after the
100 last read, or the written file mark.
102 A close will rewind the device.
104 written, then a file mark will be written before the rewind is requested.
105 On completion of the rewind an unload command will be issued.
106 The device is unmounted.
110 tapes may run in either
114 block-size modes. Most
116 devices run in fixed block-size mode, where most nine-track tapes and
117 many new cartridge formats allow variable block-size.
118 The difference between the two is as follows:
120 .It Variable block-size:
121 Each write made to the device results in a single logical record
123 One can never read or write
125 of a record from tape (though you may request a larger block and read
126 a smaller record); nor can one read multiple blocks.
127 Data from a single write is therefore read by a single read.
129 may be any value supported by the device, the
131 adapter and the system (usually between 1 byte and 64 Kbytes,
134 When reading a variable record/block from the tape, the head is
135 logically considered to be immediately after the last item read,
136 and before the next item after that.
137 If the next item is a file mark,
138 but it was never read, then the next
139 process to read will immediately hit the file mark and receive an end-of-file notification.
140 .It Fixed block-size:
141 Data written by the user is passed to the tape as a succession of
143 It may be contiguous in memory, but it is
144 considered to be a series of independent blocks.
146 an amount of data that is not an exact multiple of the blocksize.
147 One may read and write the same data as a different set of records.
148 In other words, blocks that were written together may be read separately,
151 If one requests more blocks than remain in the file, the drive will
152 encounter the file mark.
153 As there is some data to return (unless
154 there were no records before the file mark), the read will succeed,
156 The next read will return immediately with a value
158 (As above, if the file mark is never read, it remains for the next
159 process to read if in no-rewind mode.)
161 .Sh FILE MARK HANDLING
162 The handling of file marks on write is automatic.
164 written to the tape, and has not done a read since the last write,
165 then a file mark will be written to the tape when the device is
167 If a rewind is requested after a write, then the driver
168 assumes that the last file on the tape has been written, and ensures
169 that there are two file marks written to the tape.
171 this is that there seems to be a standard (which we follow, but don't
172 understand why) that certain types of tape do not actually write two
173 file marks to tape, but when read, report a `phantom' file mark when the
175 These devices include the QIC family of devices.
176 (It might be that this set of devices is the same set as that of fixed
178 This has not been determined yet, and they are treated
179 as separate behaviors by the driver at this time.)
183 driver supports all of the ioctls of
186 .Bl -tag -width /dev/[n][e]sa[0-9] -compact
187 .It Pa /dev/[n][e]sa[0-9]
194 Eject on close (if capable)
196 Control mode device (to examine state while another program is
197 accessing the device, e.g.).
200 This driver lacks many of the hacks required to deal with older devices.
203 devices may not work properly with this driver yet.
205 Additionally, certain
206 tapes (QIC tapes mostly) that were written under
209 aren't automatically read correctly with this driver: you may need to
210 explicitly set variable block mode or set to the blocksize that works best
211 for your device in order to read tapes written under
215 Fine grained density and compression mode support that is bound to specific
216 device names needs to be added.
218 Support for fast indexing by use of partitions is missing.
228 driver was written for the
235 Many ideas were gleaned from the
237 device driver written and ported from
241 .An Julian Elischer .
243 The current owner of record is
245 who has suffered too many
246 years of breaking tape drivers.