SCSI tape drive and compression
I have yet another alpha question. As before, I'm running a DEC Alphastation
250 with Debian testing. The kernel is 2.4.13 with devfs and SCSI tape
drivers built into the kernel, and the SCSI driver is an NCR53c810.
I'm attempting to dump the entire machine to a DEC tape drive (TLZ07). It's a
DDS2 drive, so the tape capacity is 4GB native, 8 compressed. The machine has
two drives, a 2 GB internal and 4 GB external. The total disc space used on
both comes to 4.0 GB. However, I cannot dump all the contents to the tape
drive. It get about 3.8 GB on the tape, then claims it is full.
The drive has hardware compression, and I always used the correct device
under DEC Unix (it was /dev/nrt0h), and the both drives fit on a single tape.
Under linux, it's obvious I'm not using hardware compression. I'm using the
/dev/tapes/tape0/mtn device. There are other devices listed in the same
directory (mtan, mtmn, and mtlm) but none exist. The command,
mt -f /dev/tapes/tape0/mtn datcompression
gives
Compression off.
Compression capable.
Decompression capable.
How do I turn on the data compression? The mt man page indicates that
mt -f /dev/tapes/tape0/mtn datcompression [x]
where x is any number but 0 or 1 should turn on compression. However, all it
does is spit the "Compression off" lines out again. In fact, I'm not even
sure if this is something that can be turned on from the command line. I
would figure I have to have the correct device in /dev.
Marty Sanborn
--
| Martin Sanborn - Dept. of Chemical Engineering - Northwestern University |
| m-sanborn@nwu.edu - (847)467-1653 - http://zeolites.cqe.nwu.edu/marty |
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