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The st device driver is an interface to various SCSI tape devices. Supported tape devices include 1/4’ Tandberg 2.5 Gigabyte QIC tape drive, 1/4’ Archive Viper QIC-150 streaming tape drive, 1/4’ Emulex MT-02 tape controller, HP-88780 1/2’ tape drive, Exabyte EXB-8200/8500/8505/8505XL 8mm cartridge tape, and the Archive Python 4 mm DAT tape subsystem. st provides a standard interface to these various devices; see mtio(7I) for details.
The driver can be opened with either rewind on close or no rewind on close
options. It can also be opened with the O_NDELAY
(see open(2)
) option
when there is no tape inserted in the drive. A maximum of four tape formats
per device are supported (see FILES below). The tape format is specified
using the device name. Often tape format is also referred to as tape density.
If the driver is opened for reading in a different format
than the tape is written in, the driver overrides the user-selected format.
For example, if a 1/4’ cartridge tape is written in QIC-24 format and opened
for reading in QIC-150, the driver will detect a read failure on the first
read and automatically switch to QIC-24 to read the data.
Note that if the low density format is used, no indication is given that the driver has overridden the user-selected format. Other formats issue a warning message to inform the user of an overridden format selection. Some devices automatically perform this function and do not require driver support (1/2’ reel tape drive, for example).
Writing from the beginning of tape is performed in the user-specified format. The original tape format is used for appending onto previously written tapes.
The st tape driver has a built-in configuration table for all Sun supported tape drives. In order to support the addition of third party tape devices or to override a built-in configuration, drive information can be supplied in st.conf as global properties that apply to each node, or as properties that are applicable to one node only. The st driver looks for the property called ‘tape-config-list’. The value of this property is a list of triplets, where each triplet consists of three strings.
The formal syntax is:
tape-config-list = <triplet> [, <triplet> *]; where <triplet> := <vid+pid>, <pretty print>, <data-property-name> and <data-property-name> = <version>, <type>, <bsize>, <options>, <number of densities>, <density> [, <density>*], <default-density>;
Note that a semicolon (;) is used to terminate a prototype devinfo node specification. Individual elements listed within the specification should not be separated by a semicolon. (Refer to driver.conf(4) for more information.)
<vid+pid> is the string that is returned by the tape device on a SCSI inquiry command. This string may contain any character in the range 0x20-0x7e. Characters such as ‘ " ’ (double quote) or ‘ ’ ’ (single quote), which are not permitted in property value strings, are represented by their octal equivalent (for example, \042 and \047). Trailing spaces may be truncated.
<pretty print> is used to report the device on the console. This string may have zero length, in which case the <vid+pid> will be used to report the device.
<data-property-name> is the name of the property which contains all the tape configuration values (such as <type>, <bsize>, etc.) corresponding for the tape drive for the specified <vid+pid>.
<version> is a version number and should be 1. In the future, higher version numbers may be used to allow for changes in the syntax of the <data-property-name> value list.
<type> is a type field. Valid types are defined in /usr/include/sys/mtio.h. For third party tape configuration, the following generic types are recommended:
MT_ISQIC 0x32 MT_ISREEL 0x33 MT_ISDAT 0x34 MT_IS8MM 0x35 MT_ISOTHER 0x36
<bsize> is the preferred block size of the tape device. The value should be 0 for variable block size drives.
<options> is a bit pattern representing the drive options, as defined in /usr/include/sys/scsi/targets/stdef.h. Valid flags for tape configuration are:
ST_VARIABLE 0x0001 ST_QIC 0x0002 ST_REEL 0x0004 ST_BSF 0x0008 ST_BSR 0x0010 ST_LONG_ERASE 0x0020 ST_AUTODEN_OVERRIDE 0x0040 ST_NOBUF 0x0080 ST_KNOWS_EOD 0x0200 ST_UNLOADABLE 0x0400 ST_SOFT_ERROR_REPORTING 0x0800 ST_LONG_TIMEOUTS 0x1000 ST_BUFFERED_WRITES 0x4000 ST_NO_RECSIZE_LIMIT 0x8000 ST_MODE_SEL_COMP 0x10000
- ST_VARIABLE
- The flag indicates the tape device supports variable length record sizes.
- ST_QIC
- The flag indicates a Quarter Inch Cartridge (QIC ) tape device.
- ST_REEL
- The flag indicates a 1/2-inch reel tape device.
- ST_BSF
If flag is set, the device supports backspace over EOF marks (bsf - see mt(1) ).
- ST_BSR
- If flag is set, the tape device supports the backspace record operation (bsr - see mt(1) ). If the device does not support bsr, the st driver emulates the action by rewinding the tape and using the forward space record (fsf) operation to forward the tape to the correct file. The driver then uses forward space record (fsr - see mt(1) ) to forward the tape to the correct record.
- ST_LONG_ERASE
- The flag indicates the tape device needs a longer time than normal to erase.
- ST_AUTODEN_OVERRIDE
- The auto-density override flag. The device is capable of determining the tape density automatically without issuing a ‘mode-select’/‘mode-sense command’.
- ST_NOBUF
- The flag disables the device’s ability to perform buffered writes. A buffered write occurs when the device acknowledges the completion of a write request after the data has been written to the device’s buffer, but before all of the data has been written to the tape.
- ST_KNOWS_EOD
- If flag is set, the device can determine when EOD (End of Data) has been reached. When this flag is set, the st driver uses fast file skipping. Otherwise, file skipping happens one file at a time.
- ST_UNLOADABLE
- The flag indicates the device will not complain if the st driver is unloaded and loaded again (see modload(1M) and modunload(1M) ). That is, the driver will return the correct inquiry string.
- ST_SOFT_ERROR_REPORTING
- The flag indicates the tape device will perform a ‘request sense’ or ‘log sense’ command when the device is closed. Currently, only Exabyte and DAT drives support this feature.
- ST_LONG_TIMEOUTS
- The flag indicates the tape device requires timeouts that are 5 times longer than usual for normal operation.
- ST_BUFFERED_WRITES
- If the flag is set, when data is written to the tape device, the data is buffered by the driver. The application may receive acknowledgement of completion of the write request before the data has been written to tape.
- ST_NO_RECSIZE_LIMIT
- The flag applies to variable-length tape devices. If this flag is set, the record size is not limited to a 64 Kbyte record size. The record size is only limited by the smaller of either the record size supported by the device or the maximum DMA transfer size of the system. (Refer to Large Record Sizes and WARNINGS.)
- ST_MODE_SEL_COMP
- If the ST_MODE_SEL_COMP flag is set, the driver uses the Device Configuration mode page (0x10) to enable or disable compression. The driver does not support the Data Compression mode page (0x0F) for enabling or disabling compression. This bit is only needed for those tape devices which do not support enabling compression via density codes. If the "c" or "u" device is used, compression will be enabled. If any other device density is used, it will be disabled.
<number of densities> is the number of densities specified. Each tape drive can support up to four densities. The value entered should therefore be between 1 and 4; if less than 4, the remaining densities will be assigned a value of 0x0.
<density> is a single-byte hexadecimal number. It can either be found in the drive specification manual or be obtained from the drive vendor.
<default-density> has a value between 0 and (<number of densities> - 1).
The behavior of SCSI tape positioning ioctls is the same across all devices which support them. (Refer to mtio(7I) .) However, not all devices support all ioctls. The driver returns an ENOTTY error on unsupported ioctls.
The retension ioctl only applies to 1/4’ cartridge tape devices. It is used to restore tape tension, thus improving the tape’s soft error rate after extensive start-stop operations or long-term storage.
In order to increase performance
of variable-length tape devices (particularly when they are used to read/write
small record sizes), two operations in the MTIOCTOP
ioctl, MTSRSZ
and
MTGRSZ
, can be used to set and get fixed record lengths. The ioctl also
works with fixed-length tape drives which allow multiple record sizes. The
min/max limits of record size allowed on a driver are found by using a
SCSI
-2 READ
command to the drive. If this command fails, the default min/max
record sizes allowed are 1 byte and 63k bytes. An application that needs
to use a different record size opens the device, sets the size with the
MTSRSZ
ioctl, and then continues with I/O. The scope of the change in record
size remains until the device is closed.
The next open to the device resets the record size to the default record
size (retrieved from st.conf).
Note that the error status is reset by the MTIOCGET get status ioctl call or by the next read, write, or other ioctl operation. If no error has occurred (sense key is 0), the current file and record position is returned.
tape-config-list =
"Magic DAT", "Magic 4mm Helical Scan", "magic-data";
magic-data = 1,0x34,1024,0x1639,4,0,0x8c,0x8c,0x8c,3;
name="st" class="scsi"
target=0 lun=0;
name="st" class="scsi"
target=1 lun=0;
name="st" class="scsi"
target=2 lun=0;
.
.
.
name="st" class="scsi"
target=6 lun=0;
name="st" class="scsi"
target=0 lun=0;
name="st" class="scsi"
target=1 lun=0;
name="st" class="scsi"
target=2 lun=0
tape-config-list =
"Magic DAT", "Magic 4mm Helical Scan", "magic-data"
magic-data = 1,0x34,1024,0x1639,4,0,0x8c,0x8c,0x8c,3;
name="st" class="scsi"
target=3 lun=0;
.
.
.
name="st" class="scsi"
target=6 lun=0;
If this flag is set, the st driver issues a SCSI -2 READ command to the device to determine the maximum record size allowed by it. If the command fails, st continues to use the maximum record sizes mentioned in the mtio(7I) man page.
If the command succeeds, st restricts the maximum transfer size of a variable-length device to the minimum of that record size and the maximum DMA size that the host adapter can handle. Fixed-length devices are bound by the maximum DMA size allocated by the machine. Note that tapes created with a large record size may not be readable by earlier releases or on other platforms.
(Refer to the WARNINGS section for more information.)
The Emulex drives have only a physical end of tape (PEOT ); thus it is not possible to write past EOT . All other drives have a logical end of tape (LEOT ) before PEOT to guarantee flushing the data onto the tape. The amount of storage between LEOT and PEOT varies from less than 1 Mbyte to about 20 Mbyte, depending on the tape drive.
If EOT is encountered while writing an Emulex, no error is reported but the number of bytes transferred is 0 and no further writing is allowed. On all other drives, the first write that encounters EOT will return a short count or 0. If a short count is returned, then the next write will return 0. After a zero count is returned, the next write returns a full count or short count. A following write returns 0 again. It is important that the number and size of trailer records be kept as small as possible to prevent data loss. Therefore, writing after EOT is not recommended.
Reading past EOT is transparent to the user. Reading is stopped only by reading EOF ’s. For 1/2’ reel devices, it is possible to read off the end of the reel if one reads past the two file marks which mark the end of recorded media.
In order for write buffering to work properly, sufficient space after LEOT must be available to empty the write buffers. Older tape devices usually do not have sufficient space after LEOT .
To turn on tape buffering, a property in st.conf called "tape-driver-buffering" should be added. The value assigned to this property is the maximum number of buffered write requests allowed. For example, 0 indicates no write request buffering allowed, while 2 indicates buffer up to 2 write requests. If this property is not specified in st.conf, the driver defaults to a value of 0. The maximum size of write request that can be buffered is specified through a property in st.conf called "tape-driver-buf-max-size". If this property is not specified in st.conf, the driver defaults the buffer size to a value of 1 Mbyte.
An
example of st.conf, where the maximum number of write requests buffered
is 4 and maximum size of write request buffered is 2 Mbyte, is given below.
This applies to all nodes in this conf file.
tape-driver-buffering = 4; tape-driver-buf-max-size = 0x200000;
name="st" class="scsi"
target=0 lun=0;
name="st" class="scsi" target=1 lun=0;
name="st" class="scsi" target=2 lun=0;
...
In the case of a SCSI bus reset, a medium error, or any other fatal transport error on a buffered request, the driver returns an error on subsequent write requests and allows no more writes. If no further write requests occur, an error is returned on close.
Since some applications may perceive write buffering as a potential data integrity problem, this feature is disabled by default and needs to be explicitly enabled in the config entry and turned on by means of the property in st.conf. Furthermore, some fault tolerant backup servers make assumptions about the data buffering in the tape drive itself. These assumptions may not be valid if write buffering has been enabled.
Write buffering may be superseded by other performance enhancements in a future release.
For 1/2’ reel tape devices (HP
-88780), the densities are:
l 800 BPI density m 1600 BPI density h 6250 BPI density c data compression (not supported on all modules)
l Standard 2 Gbyte format m 5 Gbyte format (8500, 8505 only) h,c 5 Gbyte compressed format (8505 only)
l Standard format m,h,c data compression
l,m,h,c density of the tape cartridge type (not all devices can read and write all formats)
l QIC-11 Format m,h,c QIC-24 Format
Error for command ’<command name>’Error Level: Fatal Requested Block <n>, Error Block: <m> Sense Key: <sense key name> Vendor ’<name>’: ASC = 0x<a> (<extended sense code name>), ASCQ = 0x<b>, FRU = 0x<c>The command indicated by <command name> failed. The Requested Block is the block where the transfer started and the Error Block is the block that caused the error. Sense Key, ASC, ASCQ and FRU information is returned by the target in response to a request sense command.
write/read: not modulo <n> block sizeThe request size for fixed record size devices must be a multiple of the specified block size.
recovery by resets failed After a transport error, the driver attempted to recover with device and bus reset. This recovery failed.
Periodic head cleaning required The driver reported that periodic head cleaning is now required.
Soft error rate (<n>%) during writing/reading was too high The soft error rate has exceeded the threshold specified by the vendor.
SCSI transport failed: reason ’xxxx’: {retrying|giving up} The host adapter has failed to transport a command to the target for the reason stated. The driver will either retry the command or, ultimately, give up.
The ST_NO_RECSIZE_LIMIT flag can be disabled in the config entry for the drive as a work-around. (Refer to Tape Configuration.) This action disables the ability to read and write with large block sizes and allows the reading of tapes written prior to Solaris 2.4 with large block sizes.
(Refer to mtio(7I) for a description of maximum record sizes.)
Tape devices that do not return a BUSY status during tape loading prevent user commands from being held until the device is ready. The user must delay issuing any tape operations until the tape device is ready. This is not a problem for tape devices supplied by Sun Microsystems Computer Corporation.
Tape devices that do not report a blank check error at the end of recorded media may cause file positioning operations to fail. Some tape drives, for example, mistakenly report media error instead of blank check error.