Dan Langille wrote:
On 2 Apr 2006 at 0:32, Erik P. Olsen wrote:
If I set compression on on my DDS-4 tape device do I then again have to label
the tapes that were previously labeled with compression off? I fear that the
hardware switches compression off if it sees uncompressed data (the label) on
the tapes.
I think not.
Test it. Set compression on, then do a restore from an old tape. I
think it will be fine. The tape drive recognizes the compression, or
should.
OK, I tested it. The tape was a newly labeled tape and it has been labeled with
h/w compression off. Compression was then set to on by "mt defcompression 1" and
a subsequent "tapeinfo -f /dev/sg2" confirmed that "DataCompCapable: yes".
S/W compression was then removed from the FileSet directives and a back-up run
started. After the jobs were finished it was realized that approx. the same
amount of bytes read were indeed written to the tape. In other words the
compression was set to off presumably because the tape had been written with
compression off prior to the back-up jobs.
I therefore assume that I'll have to erase the tapes, set h/w compression to on
and then label the tape again. It should then have the label written compressed
and possibly the back-up will be written compressed to the tape. I'll test that
as well.
--
Regards,
Erik P. Olsen.
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