9.3. Tape driver (st)
The tape driver interface is documented in the file
/usr/src/linux/drivers/scsi/README.st and on the
st(4) man page (type man st). The file
README.st also documents the different parameters and
options of the driver together with the basic mechanisms used in the driver.
The tape driver is usually accessed via the mt command
(see man mt). mtx is an associated
program for controlling tape autoloaders
(see
mtx.sourceforge.net).
The st driver detects those SCSI devices whose peripheral device type
is "Sequential-access" (code number 1) unless they appear on the
driver's "reject_list". [Currently the OnStream tape drives (described
in a following section) are the only entry in this reject_list.]
The st driver is capable of recognizing 32 tape drives. There are
8 device file names for each tape drive: a rewind and non-rewind
variant for each of 4 modes (numbered 0 to 3). See the tape device
file name examples in Section 3.2 on device names. Any number of
tape drives (up to the overall limit of 32) can be added after the st
driver is loaded.
ATAPI tape drives can be controlled by this driver with help from the
ide-scsi pseudo adapter driver. The discussion in Section 9.2.4
also applies for ATAPI tape drives (and ATAPI floppies).
9.3.1. st boot parameters
st=xxx[,yyy] where xxx is one of the following:
buffer_kbs:<n>
write_threshold_kbs:<n>
max_buffers:<n>
max_sg_segs:<n>
(The old boot parameters st=aa[,bb[,cc[,dd]]] supported but deprecated)
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The default driver buffer size (buffer_kbs) is 32 (i.e. 32 KB).
The default asynchronous write threshold (write_threshold_kbs) is 30
(i.e. 30 KB).
The default number of buffers allocated at initialization (max_buffers)
is 4.
The default number of scatter/gather segments to use (max_sg_segs) is
32.
9.3.2. st module parameters
buffer_kbs=<n>
write_threshold_kbs=<n>
max_buffers=<n>
max_sg_segs=<n>
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9.3.3. st proc interface
None.
9.3.4. osst driver for OnStream devices
There is an auxiliary tape driver for tape drives manufactured by
OnStream. It is an additional upper level driver and can co-exist with
the st driver. Its driver name is "osst" (as is its module name).
The OnStream SC-x0 SCSI tape drives can not be driven by the
standard st driver, but instead need this special osst driver and
use the /dev/osst<x> char device nodes (major 206).
[Where <x> follows the same naming scheme as st devices outlined
in Section 3.2.]
Via usb-storage and ide-scsi, you may be able to drive the USB-x0
and DI-x0 drives as well. Note that there is also a second generation
of OnStream tape drives (ADR-x0) that supports the standard SCSI-2
commands for tapes (QIC-157) and can be driven by the standard
driver st. For more information, you may have a look at the kernel
source file /usr/src/linux/drivers/scsi/README.osst.
More info on the OnStream driver may be found on
linux1.onstream.nl/test/.