1st(4) Kernel Interfaces Manual st(4)
2
6 st - SCSI tape device
7
9 #include <sys/mtio.h>
10 int ioctl(int fd, int request [, (void *)arg3]);
12 int ioctl(int fd, MTIOCTOP, (struct mtop *)mt_cmd);
13 int ioctl(int fd, MTIOCGET, (struct mtget *)mt_status);
14 int ioctl(int fd, MTIOCPOS, (struct mtpos *)mt_pos);
15
17 The st driver provides the interface to a variety of SCSI tape devices.
18 Currently, the driver takes control of all detected devices of type
19 “sequential-access”. The st driver uses major device number 9.
20 Each device uses eight minor device numbers. The lowermost five bits
22 in the minor numbers are assigned sequentially in the order of detec‐
23 tion. In the 2.6 kernel, the bits above the eight lowermost bits are
24 concatenated to the five lowermost bits to form the tape number. The
25 minor numbers can be grouped into two sets of four numbers: the princi‐
26 pal (auto-rewind) minor device numbers, n, and the “no-rewind” device
27 numbers, (n + 128). Devices opened using the principal device number
28 will be sent a REWIND command when they are closed. Devices opened us‐
29 ing the “no-rewind” device number will not. (Note that using an auto-
30 rewind device for positioning the tape with, for instance, mt does not
31 lead to the desired result: the tape is rewound after the mt command
32 and the next command starts from the beginning of the tape).
33 Within each group, four minor numbers are available to define devices
35 with different characteristics (block size, compression, density, etc.)
36 When the system starts up, only the first device is available. The
37 other three are activated when the default characteristics are defined
38 (see below). (By changing compile-time constants, it is possible to
39 change the balance between the maximum number of tape drives and the
40 number of minor numbers for each drive. The default allocation allows
41 control of 32 tape drives. For instance, it is possible to control up
42 to 64 tape drives with two minor numbers for different options.)
43 Devices are typically created by:
45 mknod -m 666 /dev/st0 c 9 0
47 mknod -m 666 /dev/st0l c 9 32
48 mknod -m 666 /dev/st0m c 9 64
49 mknod -m 666 /dev/st0a c 9 96
50 mknod -m 666 /dev/nst0 c 9 128
51 mknod -m 666 /dev/nst0l c 9 160
52 mknod -m 666 /dev/nst0m c 9 192
53 mknod -m 666 /dev/nst0a c 9 224
54 There is no corresponding block device.
56 The driver uses an internal buffer that has to be large enough to hold
58 at least one tape block. Before Linux 2.1.121, the buffer is allocated
59 as one contiguous block. This limits the block size to the largest
60 contiguous block of memory the kernel allocator can provide. The limit
61 is currently 128 kB for 32-bit architectures and 256 kB for 64-bit ar‐
62 chitectures. In newer kernels the driver allocates the buffer in sev‐
63 eral parts if necessary. By default, the maximum number of parts is
64 16. This means that the maximum block size is very large (2 MB if al‐
65 location of 16 blocks of 128 kB succeeds).
66 The driver's internal buffer size is determined by a compile-time con‐
68 stant which can be overridden with a kernel startup option. In addi‐
69 tion to this, the driver tries to allocate a larger temporary buffer at
70 run time if necessary. However, run-time allocation of large contigu‐
71 ous blocks of memory may fail and it is advisable not to rely too much
72 on dynamic buffer allocation before Linux 2.1.121 (this applies also to
73 demand-loading the driver with kerneld or kmod).
74 The driver does not specifically support any tape drive brand or model.
76 After system start-up the tape device options are defined by the drive
77 firmware. For example, if the drive firmware selects fixed-block mode,
78 the tape device uses fixed-block mode. The options can be changed with
79 explicit ioctl(2) calls and remain in effect when the device is closed
80 and reopened. Setting the options affects both the auto-rewind and the
81 nonrewind device.
82 Different options can be specified for the different devices within the
84 subgroup of four. The options take effect when the device is opened.
85 For example, the system administrator can define one device that writes
86 in fixed-block mode with a certain block size, and one which writes in
87 variable-block mode (if the drive supports both modes).
88 The driver supports tape partitions if they are supported by the drive.
90 (Note that the tape partitions have nothing to do with disk partitions.
91 A partitioned tape can be seen as several logical tapes within one
92 medium.) Partition support has to be enabled with an ioctl(2). The
93 tape location is preserved within each partition across partition
94 changes. The partition used for subsequent tape operations is selected
95 with an ioctl(2). The partition switch is executed together with the
96 next tape operation in order to avoid unnecessary tape movement. The
97 maximum number of partitions on a tape is defined by a compile-time
98 constant (originally four). The driver contains an ioctl(2) that can
99 format a tape with either one or two partitions.
100 Device /dev/tape is usually created as a hard or soft link to the de‐
102 fault tape device on the system.
103 Starting from Linux 2.6.2, the driver exports in the sysfs directory
105 /sys/class/scsi_tape the attached devices and some parameters assigned
106 to the devices.
107 Data transfer
109 The driver supports operation in both fixed-block mode and variable-
110 block mode (if supported by the drive). In fixed-block mode the drive
111 writes blocks of the specified size and the block size is not dependent
112 on the byte counts of the write system calls. In variable-block mode
113 one tape block is written for each write call and the byte count deter‐
114 mines the size of the corresponding tape block. Note that the blocks
115 on the tape don't contain any information about the writing mode: when
116 reading, the only important thing is to use commands that accept the
117 block sizes on the tape.
118 In variable-block mode the read byte count does not have to match the
120 tape block size exactly. If the byte count is larger than the next
121 block on tape, the driver returns the data and the function returns the
122 actual block size. If the block size is larger than the byte count, an
123 error is returned.
124 In fixed-block mode the read byte counts can be arbitrary if buffering
126 is enabled, or a multiple of the tape block size if buffering is dis‐
127 abled. Before Linux 2.1.121 allow writes with arbitrary byte count if
128 buffering is enabled. In all other cases (before Linux 2.1.121 with
129 buffering disabled or newer kernel) the write byte count must be a mul‐
130 tiple of the tape block size.
131 In Linux 2.6, the driver tries to use direct transfers between the user
133 buffer and the device. If this is not possible, the driver's internal
134 buffer is used. The reasons for not using direct transfers include im‐
135 proper alignment of the user buffer (default is 512 bytes but this can
136 be changed by the HBA driver), one or more pages of the user buffer not
137 reachable by the SCSI adapter, and so on.
138 A filemark is automatically written to tape if the last tape operation
140 before close was a write.
141 When a filemark is encountered while reading, the following happens.
143 If there are data remaining in the buffer when the filemark is found,
144 the buffered data is returned. The next read returns zero bytes. The
145 following read returns data from the next file. The end of recorded
146 data is signaled by returning zero bytes for two consecutive read
147 calls. The third read returns an error.
148 Ioctls
150 The driver supports three ioctl(2) requests. Requests not recognized
151 by the st driver are passed to the SCSI driver. The definitions below
152 are from /usr/include/linux/mtio.h:
153 MTIOCTOP — perform a tape operation
155 This request takes an argument of type (struct mtop *). Not all drives
156 support all operations. The driver returns an EIO error if the drive
157 rejects an operation.
158 /* Structure for MTIOCTOP - mag tape op command: */
160 struct mtop {
161 short mt_op; /* operations defined below */
162 int mt_count; /* how many of them */
163 };
164 Magnetic tape operations for normal tape use:
166 MTBSF Backward space over mt_count filemarks.
168 MTBSFM Backward space over mt_count filemarks. Reposition the tape to
170 the EOT side of the last filemark.
171 MTBSR Backward space over mt_count records (tape blocks).
173 MTBSS Backward space over mt_count setmarks.
175 MTCOMPRESSION
177 Enable compression of tape data within the drive if mt_count is
178 nonzero and disable compression if mt_count is zero. This com‐
179 mand uses the MODE page 15 supported by most DATs.
180 MTEOM Go to the end of the recorded media (for appending files).
182 MTERASE
184 Erase tape. With Linux 2.6, short erase (mark tape empty) is
185 performed if the argument is zero. Otherwise, long erase (erase
186 all) is done.
187 MTFSF Forward space over mt_count filemarks.
189 MTFSFM Forward space over mt_count filemarks. Reposition the tape to
191 the BOT side of the last filemark.
192 MTFSR Forward space over mt_count records (tape blocks).
194 MTFSS Forward space over mt_count setmarks.
196 MTLOAD Execute the SCSI load command. A special case is available for
198 some HP autoloaders. If mt_count is the constant
199 MT_ST_HPLOADER_OFFSET plus a number, the number is sent to the
200 drive to control the autoloader.
201 MTLOCK Lock the tape drive door.
203 MTMKPART
205 Format the tape into one or two partitions. If mt_count is pos‐
206 itive, it gives the size of partition 1 and partition 0 contains
207 the rest of the tape. If mt_count is zero, the tape is format‐
208 ted into one partition. From Linux 4.6, a negative mt_count
209 specifies the size of partition 0 and the rest of the tape con‐
210 tains partition 1. The physical ordering of partitions depends
211 on the drive. This command is not allowed for a drive unless
212 the partition support is enabled for the drive (see
213 MT_ST_CAN_PARTITIONS below).
214 MTNOP No op—flushes the driver's buffer as a side effect. Should be
216 used before reading status with MTIOCGET.
217 MTOFFL Rewind and put the drive off line.
219 MTRESET
221 Reset drive.
222 MTRETEN
224 Re-tension tape.
225 MTREW Rewind.
227 MTSEEK Seek to the tape block number specified in mt_count. This oper‐
229 ation requires either a SCSI-2 drive that supports the LOCATE
230 command (device-specific address) or a Tandberg-compatible
231 SCSI-1 drive (Tandberg, Archive Viper, Wangtek, ...). The block
232 number should be one that was previously returned by MTIOCPOS if
233 device-specific addresses are used.
234 MTSETBLK
236 Set the drive's block length to the value specified in mt_count.
237 A block length of zero sets the drive to variable block size
238 mode.
239 MTSETDENSITY
241 Set the tape density to the code in mt_count. The density codes
242 supported by a drive can be found from the drive documentation.
243 MTSETPART
245 The active partition is switched to mt_count. The partitions
246 are numbered from zero. This command is not allowed for a drive
247 unless the partition support is enabled for the drive (see
248 MT_ST_CAN_PARTITIONS below).
249 MTUNLOAD
251 Execute the SCSI unload command (does not eject the tape).
252 MTUNLOCK
254 Unlock the tape drive door.
255 MTWEOF Write mt_count filemarks.
257 MTWSM Write mt_count setmarks.
259 Magnetic tape operations for setting of device options (by the supe‐
261 ruser):
262 MTSETDRVBUFFER
264 Set various drive and driver options according to bits encoded
265 in mt_count. These consist of the drive's buffering mode, a set
266 of Boolean driver options, the buffer write threshold, defaults
267 for the block size and density, and timeouts (only since Linux
268 2.1). A single operation can affect only one item in the list
269 below (the Booleans counted as one item.)
270 A value having zeros in the high-order 4 bits will be used to
272 set the drive's buffering mode. The buffering modes are:
273 0 The drive will not report GOOD status on write commands
275 until the data blocks are actually written to the medium.
276 1 The drive may report GOOD status on write commands as
278 soon as all the data has been transferred to the drive's
279 internal buffer.
280 2 The drive may report GOOD status on write commands as
282 soon as (a) all the data has been transferred to the
283 drive's internal buffer, and (b) all buffered data from
284 different initiators has been successfully written to the
285 medium.
286 To control the write threshold the value in mt_count must in‐
288 clude the constant MT_ST_WRITE_THRESHOLD bitwise ORed with a
289 block count in the low 28 bits. The block count refers to
290 1024-byte blocks, not the physical block size on the tape. The
291 threshold cannot exceed the driver's internal buffer size (see
292 DESCRIPTION, above).
293 To set and clear the Boolean options the value in mt_count must
295 include one of the constants MT_ST_BOOLEANS, MT_ST_SETBOOLEANS,
296 MT_ST_CLEARBOOLEANS, or MT_ST_DEFBOOLEANS bitwise ORed with
297 whatever combination of the following options is desired. Using
298 MT_ST_BOOLEANS the options can be set to the values defined in
299 the corresponding bits. With MT_ST_SETBOOLEANS the options can
300 be selectively set and with MT_ST_DEFBOOLEANS selectively
301 cleared.
302 The default options for a tape device are set with MT_ST_DEF‐
304 BOOLEANS. A nonactive tape device (e.g., device with minor 32
305 or 160) is activated when the default options for it are defined
306 the first time. An activated device inherits from the device
307 activated at start-up the options not set explicitly.
308 The Boolean options are:
310 MT_ST_BUFFER_WRITES (Default: true)
312 Buffer all write operations in fixed-block mode. If this
313 option is false and the drive uses a fixed block size,
314 then all write operations must be for a multiple of the
315 block size. This option must be set false to write reli‐
316 able multivolume archives.
317 MT_ST_ASYNC_WRITES (Default: true)
319 When this option is true, write operations return immedi‐
320 ately without waiting for the data to be transferred to
321 the drive if the data fits into the driver's buffer. The
322 write threshold determines how full the buffer must be
323 before a new SCSI write command is issued. Any errors
324 reported by the drive will be held until the next opera‐
325 tion. This option must be set false to write reliable
326 multivolume archives.
327 MT_ST_READ_AHEAD (Default: true)
329 This option causes the driver to provide read buffering
330 and read-ahead in fixed-block mode. If this option is
331 false and the drive uses a fixed block size, then all
332 read operations must be for a multiple of the block size.
333 MT_ST_TWO_FM (Default: false)
335 This option modifies the driver behavior when a file is
336 closed. The normal action is to write a single filemark.
337 If the option is true, the driver will write two file‐
338 marks and backspace over the second one.
339 Note: This option should not be set true for QIC tape
341 drives since they are unable to overwrite a filemark.
342 These drives detect the end of recorded data by testing
343 for blank tape rather than two consecutive filemarks.
344 Most other current drives also detect the end of recorded
345 data and using two filemarks is usually necessary only
346 when interchanging tapes with some other systems.
347 MT_ST_DEBUGGING (Default: false)
349 This option turns on various debugging messages from the
350 driver (effective only if the driver was compiled with
351 DEBUG defined nonzero).
352 MT_ST_FAST_EOM (Default: false)
354 This option causes the MTEOM operation to be sent di‐
355 rectly to the drive, potentially speeding up the opera‐
356 tion but causing the driver to lose track of the current
357 file number normally returned by the MTIOCGET request.
358 If MT_ST_FAST_EOM is false, the driver will respond to an
359 MTEOM request by forward spacing over files.
360 MT_ST_AUTO_LOCK (Default: false)
362 When this option is true, the drive door is locked when
363 the device file is opened and unlocked when it is closed.
364 MT_ST_DEF_WRITES (Default: false)
366 The tape options (block size, mode, compression, etc.)
367 may change when changing from one device linked to a
368 drive to another device linked to the same drive depend‐
369 ing on how the devices are defined. This option defines
370 when the changes are enforced by the driver using SCSI-
371 commands and when the drives auto-detection capabilities
372 are relied upon. If this option is false, the driver
373 sends the SCSI-commands immediately when the device is
374 changed. If the option is true, the SCSI-commands are
375 not sent until a write is requested. In this case, the
376 drive firmware is allowed to detect the tape structure
377 when reading and the SCSI-commands are used only to make
378 sure that a tape is written according to the correct
379 specification.
380 MT_ST_CAN_BSR (Default: false)
382 When read-ahead is used, the tape must sometimes be
383 spaced backward to the correct position when the device
384 is closed and the SCSI command to space backward over
385 records is used for this purpose. Some older drives
386 can't process this command reliably and this option can
387 be used to instruct the driver not to use the command.
388 The end result is that, with read-ahead and fixed-block
389 mode, the tape may not be correctly positioned within a
390 file when the device is closed. With Linux 2.6, the de‐
391 fault is true for drives supporting SCSI-3.
392 MT_ST_NO_BLKLIMS (Default: false)
394 Some drives don't accept the READ BLOCK LIMITS SCSI com‐
395 mand. If this is used, the driver does not use the com‐
396 mand. The drawback is that the driver can't check before
397 sending commands if the selected block size is acceptable
398 to the drive.
399 MT_ST_CAN_PARTITIONS (Default: false)
401 This option enables support for several partitions within
402 a tape. The option applies to all devices linked to a
403 drive.
404 MT_ST_SCSI2LOGICAL (Default: false)
406 This option instructs the driver to use the logical block
407 addresses defined in the SCSI-2 standard when performing
408 the seek and tell operations (both with MTSEEK and MTIOC‐
409 POS commands and when changing tape partition). Other‐
410 wise, the device-specific addresses are used. It is
411 highly advisable to set this option if the drive supports
412 the logical addresses because they count also filemarks.
413 There are some drives that support only the logical block
414 addresses.
415 MT_ST_SYSV (Default: false)
417 When this option is enabled, the tape devices use the
418 System V semantics. Otherwise, the BSD semantics are
419 used. The most important difference between the seman‐
420 tics is what happens when a device used for reading is
421 closed: in System V semantics the tape is spaced forward
422 past the next filemark if this has not happened while us‐
423 ing the device. In BSD semantics the tape position is
424 not changed.
425 MT_NO_WAIT (Default: false)
427 Enables immediate mode (i.e., don't wait for the command
428 to finish) for some commands (e.g., rewind).
429 An example:
431 struct mtop mt_cmd;
433 mt_cmd.mt_op = MTSETDRVBUFFER;
434 mt_cmd.mt_count = MT_ST_BOOLEANS |
435 MT_ST_BUFFER_WRITES | MT_ST_ASYNC_WRITES;
436 ioctl(fd, MTIOCTOP, mt_cmd);
437 The default block size for a device can be set with
439 MT_ST_DEF_BLKSIZE and the default density code can be set with
440 MT_ST_DEFDENSITY. The values for the parameters are or'ed with
441 the operation code.
442 With Linux 2.1.x and later, the timeout values can be set with
444 the subcommand MT_ST_SET_TIMEOUT ORed with the timeout in sec‐
445 onds. The long timeout (used for rewinds and other commands
446 that may take a long time) can be set with MT_ST_SET_LONG_TIME‐
447 OUT. The kernel defaults are very long to make sure that a suc‐
448 cessful command is not timed out with any drive. Because of
449 this, the driver may seem stuck even if it is only waiting for
450 the timeout. These commands can be used to set more practical
451 values for a specific drive. The timeouts set for one device
452 apply for all devices linked to the same drive.
453 Starting from Linux 2.4.19 and Linux 2.5.43, the driver supports
455 a status bit which indicates whether the drive requests clean‐
456 ing. The method used by the drive to return cleaning informa‐
457 tion is set using the MT_ST_SEL_CLN subcommand. If the value is
458 zero, the cleaning bit is always zero. If the value is one, the
459 TapeAlert data defined in the SCSI-3 standard is used (not yet
460 implemented). Values 2–17 are reserved. If the lowest eight
461 bits are >= 18, bits from the extended sense data are used. The
462 bits 9–16 specify a mask to select the bits to look at and the
463 bits 17–23 specify the bit pattern to look for. If the bit pat‐
464 tern is zero, one or more bits under the mask indicate the
465 cleaning request. If the pattern is nonzero, the pattern must
466 match the masked sense data byte.
467 MTIOCGET — get status
469 This request takes an argument of type (struct mtget *).
470 /* structure for MTIOCGET - mag tape get status command */
472 struct mtget {
473 long mt_type;
474 long mt_resid;
475 /* the following registers are device dependent */
476 long mt_dsreg;
477 long mt_gstat;
478 long mt_erreg;
479 /* The next two fields are not always used */
480 daddr_t mt_fileno;
481 daddr_t mt_blkno;
482 };
483 mt_type
485 The header file defines many values for mt_type, but the current
486 driver reports only the generic types MT_ISSCSI1 (Generic SCSI-1
487 tape) and MT_ISSCSI2 (Generic SCSI-2 tape).
488 mt_resid
490 contains the current tape partition number.
491 mt_dsreg
493 reports the drive's current settings for block size (in the low
494 24 bits) and density (in the high 8 bits). These fields are de‐
495 fined by MT_ST_BLKSIZE_SHIFT, MT_ST_BLKSIZE_MASK, MT_ST_DEN‐
496 SITY_SHIFT, and MT_ST_DENSITY_MASK.
497 mt_gstat
499 reports generic (device independent) status information. The
500 header file defines macros for testing these status bits:
501 GMT_EOF(x)
503 The tape is positioned just after a filemark (always
504 false after an MTSEEK operation).
505 GMT_BOT(x)
507 The tape is positioned at the beginning of the first file
508 (always false after an MTSEEK operation).
509 GMT_EOT(x)
511 A tape operation has reached the physical End Of Tape.
512 GMT_SM(x)
514 The tape is currently positioned at a setmark (always
515 false after an MTSEEK operation).
516 GMT_EOD(x)
518 The tape is positioned at the end of recorded data.
519 GMT_WR_PROT(x)
521 The drive is write-protected. For some drives this can
522 also mean that the drive does not support writing on the
523 current medium type.
524 GMT_ONLINE(x)
526 The last open(2) found the drive with a tape in place and
527 ready for operation.
528 GMT_D_6250(x)
530 GMT_D_1600(x)
531 GMT_D_800(x)
532 This “generic” status information reports the current
533 density setting for 9-track ½" tape drives only.
534 GMT_DR_OPEN(x)
536 The drive does not have a tape in place.
537 GMT_IM_REP_EN(x)
539 Immediate report mode. This bit is set if there are no
540 guarantees that the data has been physically written to
541 the tape when the write call returns. It is set zero
542 only when the driver does not buffer data and the drive
543 is set not to buffer data.
544 GMT_CLN(x)
546 The drive has requested cleaning. Implemented since
547 Linux 2.4.19 and Linux 2.5.43.
548 mt_erreg
550 The only field defined in mt_erreg is the recovered error count
551 in the low 16 bits (as defined by MT_ST_SOFTERR_SHIFT and
552 MT_ST_SOFTERR_MASK). Due to inconsistencies in the way drives
553 report recovered errors, this count is often not maintained
554 (most drives do not by default report soft errors but this can
555 be changed with a SCSI MODE SELECT command).
556 mt_fileno
558 reports the current file number (zero-based). This value is set
559 to -1 when the file number is unknown (e.g., after MTBSS or MT‐
560 SEEK).
561 mt_blkno
563 reports the block number (zero-based) within the current file.
564 This value is set to -1 when the block number is unknown (e.g.,
565 after MTBSF, MTBSS, or MTSEEK).
566 MTIOCPOS — get tape position
568 This request takes an argument of type (struct mtpos *) and reports the
569 drive's notion of the current tape block number, which is not the same
570 as mt_blkno returned by MTIOCGET. This drive must be a SCSI-2 drive
571 that supports the READ POSITION command (device-specific address) or a
572 Tandberg-compatible SCSI-1 drive (Tandberg, Archive Viper, Wangtek, ...
573 ).
574 /* structure for MTIOCPOS - mag tape get position command */
576 struct mtpos {
577 long mt_blkno; /* current block number */
578 };
579
581 EACCES An attempt was made to write or erase a write-protected tape.
582 (This error is not detected during open(2).)
583 EBUSY The device is already in use or the driver was unable to allo‐
585 cate a buffer.
586 EFAULT The command parameters point to memory not belonging to the
588 calling process.
589 EINVAL An ioctl(2) had an invalid argument, or a requested block size
591 was invalid.
592 EIO The requested operation could not be completed.
594 ENOMEM The byte count in read(2) is smaller than the next physical
596 block on the tape. (Before Linux 2.2.18 and Linux 2.4.0 the ex‐
597 tra bytes have been silently ignored.)
598 ENOSPC A write operation could not be completed because the tape
600 reached end-of-medium.
601 ENOSYS Unknown ioctl(2).
603 ENXIO During opening, the tape device does not exist.
605 EOVERFLOW
607 An attempt was made to read or write a variable-length block
608 that is larger than the driver's internal buffer.
609 EROFS Open is attempted with O_WRONLY or O_RDWR when the tape in the
611 drive is write-protected.
612
614 /dev/st*
615 the auto-rewind SCSI tape devices
616 /dev/nst*
618 the nonrewind SCSI tape devices
619
621 • When exchanging data between systems, both systems have to agree on
622 the physical tape block size. The parameters of a drive after
623 startup are often not the ones most operating systems use with these
624 devices. Most systems use drives in variable-block mode if the
625 drive supports that mode. This applies to most modern drives, in‐
626 cluding DATs, 8mm helical scan drives, DLTs, etc. It may be advis‐
627 able to use these drives in variable-block mode also in Linux (i.e.,
628 use MTSETBLK or MTSETDEFBLK at system startup to set the mode), at
629 least when exchanging data with a foreign system. The drawback of
630 this is that a fairly large tape block size has to be used to get
631 acceptable data transfer rates on the SCSI bus.
632 • Many programs (e.g., tar(1)) allow the user to specify the blocking
634 factor on the command line. Note that this determines the physical
635 block size on tape only in variable-block mode.
636 • In order to use SCSI tape drives, the basic SCSI driver, a SCSI-
638 adapter driver and the SCSI tape driver must be either configured
639 into the kernel or loaded as modules. If the SCSI-tape driver is
640 not present, the drive is recognized but the tape support described
641 in this page is not available.
642 • The driver writes error messages to the console/log. The SENSE
644 codes written into some messages are automatically translated to
645 text if verbose SCSI messages are enabled in kernel configuration.
646 • The driver's internal buffering allows good throughput in fixed-
648 block mode also with small read(2) and write(2) byte counts. With
649 direct transfers this is not possible and may cause a surprise when
650 moving to the 2.6 kernel. The solution is to tell the software to
651 use larger transfers (often telling it to use larger blocks). If
652 this is not possible, direct transfers can be disabled.
653
655 mt(1)
656 The file drivers/scsi/README.st or Documentation/scsi/st.txt (kernel >=
658 2.6) in the Linux kernel source tree contains the most recent informa‐
659 tion about the driver and its configuration possibilities
660Linux man-pages 6.05 2023-02-05 st(4)