Documentation/scsi/st.rst

1 .. SPDX-License-Identifier: GPL-2.0
23 flexible method and applicable to single-user workstations. However,
27 2. The system manager (root) can define default values for some tape
32 drive performs auto-detection of the tape format well (like some
33 QIC-drives). The result is that any tape can be read, writing can be
34 continued using existing format, and the default format is used if
37 does not perform auto-detection well enough and there is a single
40 or not :-).
46 3. By default, up to four modes can be defined and selected using the minor
57 between formats in multi-tape operations (the explicitly overridden
72 limits). Both the auto-rewind (minor equals device number) and
73 non-rewind devices (minor is 128 + device number) are implemented.
86 of the tape with one or two partitions. By default support for
90 By default the driver writes one filemark when the device is closed after
128     dev_upper non-rew mode dev-lower
129     20 -  8     7    6 5  4      0
131 The non-rewind bit is always bit 7 (the uppermost bit in the lowermost
132 byte). The bits defining the mode are below the non-rewind bit. The
143 and non-rewind entries for each mode. The names are stxy and nstxy, where x
151 the defaults set by the user. The value -1 means the default is not set. The
161 directory corresponding to the mode 0 auto-rewind device (e.g., st0).
174    regular expression "^st[0-9]+$"
186       - The number of I/Os currently outstanding to this device.
188       - The amount of time spent waiting (in nanoseconds) for all I/O
193       - The number of I/Os issued to the tape drive other than read or
195         following calculation io_ms-read_ms-write_ms.
197       - The number of bytes read from the tape drive.
199       - The number of read requests issued to the tape drive.
201       - The amount of time (in nanoseconds) spent waiting for read
204       - The number of bytes written to the tape drive.
206       - The number of write requests issued to the tape drive.
208       - The amount of time (in nanoseconds) spent waiting for write
211       - The number of times during a read or write we found
212 	the residual amount to be non-zero. This should mean that a program
245 The default is BSD semantics.
252 is not possible, a driver buffer allocated at run-time is used. If
257 - one or more pages are at addresses not reachable by the HBA
258 - the number of pages in the transfer exceeds the number of
260 - one or more pages can't be locked into memory (should not happen in
268 allowed if ST_BUFFER_WRITES is non-zero and direct i/o is not used.
275 -b option) may have had good throughput but this is not true any more with
277 is to use bigger write() byte counts (e.g., tar -b 64).
286 tape after the early-warning mark to flush the driver buffer.
293 Scatter/gather buffers (buffers that consist of chunks non-contiguous
304    the size and tries again until the size of one page. The default
312    are used to extend the buffer at run-time if this is necessary. The
325 returns -1 and errno is set to ENOSPC. To enable writing a trailer,
327 bytes is returned. After this, -1 and the number of bytes are
344 			   tape drive if this is non-zero
348 set, the write threshold is set to the new buffer size - 2 kB.
363 the driver as module. If several parameters are set, the keyword-value
376   - aa is the buffer size for fixed block mode in 1024 byte units
377   - bb is the write threshold in 1024 byte units
378   - dd is the maximum number of scatter/gather segments
388 (look for a package mt-st* from the Linux ftp sites; the GNU mt does
426 	Re-tension tape.
434 	Seek to tape block count. Uses Tandberg-compatible seek (QFA)
435         for SCSI-1 drives and SCSI-2 seek for SCSI-2 drives. The file and
469 	partitions (argument non-zero). If the argument is positive,
475 	LTO drives from LTO-5 upwards. The drive has to support partitions
519 		the MTSEEK and MTIOCPOS for SCSI-2 drives instead of
549 	   Defines the default block size set automatically. Value
550 	   0xffffff means that the default is not used any more.
554 	   (0xfffff) the default will not be used any more. Otherwise
558 	   The compression default will not be used if the value of
560 	   contains the new default. If the bits 8-15 are set to a
561 	   non-zero number, and this number is not 0xff, the number is
564 	   default.
567 	   default is 900 seconds (15 minutes). The timeout should be
572 	   known to take a long time. The default is 14000 seconds
581 	   cleaning. The bits are device-dependent. The driver is
583 	   bits of the argument; must be >= 18 (values 1 - 17
585 	   a mask to select the relevant bits (the bits 9-16), and the
586 	   bit pattern (bits 17-23). If the bit pattern is zero, one
588 	   the pattern is non-zero, the pattern must match the masked
599         Tandberg-compatible QFA for SCSI-1 drives and the SCSI-2
600         command for the SCSI-2 drives.
607         block is -1 when it can't be determined (e.g., after MTBSF).
636 The MTEOM command is by default implemented as spacing over 32767
654 Debugging code is now compiled in by default but debugging is turned off
663 the driver is waiting. With the command 'ps -l' you can see the state