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Compression and TLZ07

Ayman Altounji
Valued Contributor

Compression and TLZ07

We recently moved our AlphaStation 250 from DEC Unix 4.0d to Linux (Debian linux, using the 2.4.14 kernel). This machine serves as our fileserver and has a DEC TLZ07 DDS2 DAT drive attached on the SCSI channel. I'm having trouble getting compression on the drive under Linux.

Under DEC Unix, we used the /dev/nrmt0h device, which is the no rewind compression-enable tape device. Typically, we could back the entire machine - a 2 GB internal drive and a 4 GB external drive - onto a single tape. The total data on the two drives is just over 4 GB, probably about 4.2-4.5 GB. Since switching to Linux, I cannot get any compression on the drive at all. Once 4 GB is written to the tape, it ejects.

I have attempted to modify the behavior of the drive several ways. I have tried using the standard Linux mt tools with the command "mt -f /dev/nst0 datcompress" and the enhanced mt-st tools with "mt-st -f /dev/nst0 defcompress" without success. I have also modified the stinit.def file used by stinit to initialize the drive, in which a number of modes are defined with compression on. No success with that either. What am I missing? Do I need to define a density value perhaps? Are there known problems with this drive under Linux?

Thanks for any help.