Technical data

SunOS 5.5 Devices st(7D)
ST_BUFFERED_WRITES
If the flag is set, when data is written to the tape device, the data is buf-
fered by the driver. The application may receive acknowledgementof
completion of the write request before the data has beenwritten to tape.
ST_NO_RECSIZE_LIMIT (SPARC Only)
The flag applies to variable-lengthtape 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 pages to enable or disable compression. This is only
needed for those tape devices which do not support enabling compres-
sion 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 bytehexadecimal 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).
IOCTLS The behavior of SCSI tape positioningioctls 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 aSCSI-2 READ BLOCK LIM-
ITS
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 theMTSRSZ ioctl and then continueswith 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 theMTIOCGET get status ioctl call or by the next
read, write, or other ioctl operation. If no error has occurred (sense key is zero), the
current file and record position is returned.
modified 30 Aug 1995 7D-307