Working with “mt” Commands: reading and writing to tape.
The following assumes the tape device is “/dev/st0″
STEP 1 ( rewind the tape)
# mt -f /dev/st0 rewind
STEP 2 (check to see if you are at block 0)
# mt -f /dev/st0 tell
At block 0.
STEP 3 (Backup “tar compress” directories “one” and “two”)
# tar -czf /dev/st0 one two
STEP 4 (Check to see what block you are at)
# mt -f /dev/st0 tell
You should get something like block 2 at this point.
STEP 5 (Rewind the tape)
# mt -f /dev/st0 rewind
STEP 6 (List the files)
# tar -tzf /dev/st0
one/
one/test
two/
STEP 7 (Restore directory “one” into directory “junk”). Note, you
have to first rewind the tape, since the last operation moved
ahead 2 blocks. Check this with “mt -f /dev/st0″.
# cd junk
# mt -f /dev/st0 rewind
# mt -f /dev/st0 tell
At block 0.
# tar -xzf /dev/st0 one
STEP 8 (Next, take a look to see what block the tape is at)
# mt -f /dev/st0 tell
At block 2.
STEP 9 (Now backup directories three and four)
# tar -czf /dev/st0 three four
After backing up the files, the tape should be past block 2.
Check this.
# mt -f /dev/st0 tell
At block 4.
Currently the following exist:
At block 1:
one/
one/test
two/
At block 2:
three/
three/samplehere
four/
At block 4:
(* This is empty *)
A few notes. You can set the blocking factor and a label
with tar. For example:
$ tar –label=”temp label” –create –blocking-factor=128 –file=/dev/st0 Notes
But note if you try to read it with the default, incorrect blocking
factor, then, you will get the following error:
$ tar -t –file=/dev/st0
tar: /dev/st0: Cannot read: Cannot allocate memory
tar: At beginning of tape, quitting now
tar: Error is not recoverable: exiting now
However this is easily fixed with the correct blocking factor
$ mt -f /dev/st0 rewind
$ tar -t –blocking-factor=128 –file=/dev/st0
temp label
Notes
Take advantage of the label command.
$ MYCOMMENTS=”Big_important_tape”
$ tar –label=”$(date +%F)”+”${MYCOMMENTS}”
Writing to tape on a remote 192.168.1.155 computer
$ tar cvzf - ./tmp | ssh -l chirico 192.168.1.155 ‘(mt -f /dev/st0 rewind; dd of=/dev/st0 )’
Restoring the contents from tape on a remote computer
$ ssh -l chirico 192.168.1.155 ‘(mt -f /dev/st0 rewind; dd if=/dev/st0 )’|tar xzf -
Getting data off of tape with dd command with odd blocking factor. Just set ibs very high
$ mt -f /dev/st0 rewind
$ tar –label=”Contenets of Notes” –create –blocking-factor=128 –file=/dev/st0 Notes
$ mt -f /dev/st0 rewind
$ dd ibs=1048576 if=/dev/st0 of=notes.tar
The above will probably work with ibs=64k as well
