scsitape - control SCSI tape devices
scsitape [-f <scsi-generic-device>] commands
The scsitape command controls SCSI tape drives in a platform-independent manner. As long
as 'mtx' works on the platform, so does 'scsitape'.
Note that 'scsitape' and your OS's native tape driver may stomp on each other. In particu-
lar, if you use 'setblk' and your OS's native tape driver has a different notion of the
block size, you may get evil results. It is recommended to use 'scsitape' only for soft-
ware where you've written your own low-level READ and WRITE routines that use the SCSI
command set to directly talk to tape drives (i.e., you do not use the OS's native tape
driver at all).
The first argument, given following -f , is the SCSI generic device corresponding to your
tape drive. Consult your operating system's documentation for more information (for exam-
ple, under Linux these are generally /dev/sg0 through /dev/sg15, under FreeBSD these are
/dev/pass0 through /dev/passX. Under Solaris this is usually the same as your tape drive
(Solaris has a SCSI passthrough ioctl). You can set the STAPE or TAPE environment variable
rather than use -f.
Set the tape drive's SCSI block size to <n> bytes. (NOTE: if you are using your
OS's native tape driver, THIS IS EVIL!).
fsf <n> Go forward by <n> tapemarks.
bsf <n> Go to immediately previous the <n>th previous tapemark. (WARNING: This probably
doesn't do what you expect -- e.g. if you are immediately after a tapemark and
type 'bfs 1', it moves to immediately *before* that tape mark, for a sum total
of zero effective movement!).
eod Go to end of data.
rewind Rewind the tape drive.
eject Eject the tape currently in the drive.
erase Does a *short* erase (warning: does NOT work on all drives!).
write <n> filemarks ( 'mark 0' flushes the drive's buffers ).
seek <n> Seek to a logical position <n> that was reported by a previous 'tapeinfo' com-
write blocks from stdin to the tape. Chunk the data into <blocksize>-sized
chunks. *DOES NOT WRITE OUT A TAPEMARK!* (you will need to use a subsequent mark
1 command to write out a tape mark).
read [<blocksize>] [ <#blocks/#bytes> ]
read blocks from the tape, write them to stdout. If we are in variable block
mode, <blocksize> should be zero (note: The maximum block size we currently sup-
port in variable block mode is 128K, MAX_READ_SIZE will need to be turned into a
settable variable to allow bigger reads). If <blocksize> is ommitted, we assume
that we're in variable block mode, and that we are going to read from tape until
we hit a tapemark or end of partition or end of tape.
This program was written by Eric Lee Green <email@example.com>. Major portions of the
'mtxl.c' library used herein were written by Leonard Zubkoff.
The SCSI read and write routines are based upon those that Richard Fish wrote for Enhanced
Software Technology's BRU 16.1 product, substantially modified to work in our particular
environment (in particular, all the variable block stuff is new since BRU only does fixed
block reads and writes, and the BRU code uses bitmasks rather than bitfields for the vari-
ous flags and such in return values, as well as the BRU code having a different SCSI API
and having variable names considerably shorter than the rather sesquipedalian 'mtx' iden-
tifiers). As required by 'mtxl.c', these routines are licensed under the GNU General Pub-
Under Linux, cat /proc/scsi/scsi will tell you what SCSI devices you have. You can then
refer to them as /dev/sga, /dev/sgb, etc. by the order they are reported.
Under FreeBSD, camcontrol devlist will tell you what SCSI devices you have, along with
which pass device controls them.
Under Solaris 7 and 8, /usr/sbin/devfsadm -C will clean up your /devices directory. Then
find /devices -name 'st@*' -print will return a list of all tape drives. /dev on Solaris
is apparently only of historical interest.
BUGS AND LIMITATIONS
for scsitape read 0 <n> where you are doing variable-block-size reads and wish for <n>
bytes, it instead reads one and exactly one block from tape and prints that (no matter
what its size). Use 'dd' on the output of scsitape if you want finer control.
scsitape read 0 attempts reads of MAX_READ_SIZE, which is currently 128K. If blocks on
tape are larger than 128K, only the first 128K will be read -- the remainder will be
silently dumped in the toilet.
This program does not interact well (or at all :-) with your OS's native tape driver. You
will likely see weird things happen if you attempt to intermingle scsitape commands with
native tape driver operations. Note that BRU 16.1 for Solaris (and possibly others, but
Solaris I know about) will have a 'scsi' keyword to bypass the native tape driver and
write via direct uscsi commands, so if you use BRU 16.1 to write your actual tape ar-
chives. (Assuming that BRU 16.1 has been released at the time that you read this).
This version of scsitape is currently being maintained by Eric Lee Green <firstname.lastname@example.org>
formerly of Enhanced Software Technologies Inc. as part of the 'mtx' suite of programs.
The 'mtx' home page is http://mtx.sourceforge.net and the actual code is currently avail-
able there and via CVS from http://sourceforge.net/projects/mtx .