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drive compression discovery
2003-03-10 15:30:27
Hi all,
I'm familiar with the general theory of how to "rescue" an AMANDA tape
that's been written with drive compression turned on. Here's my
situation:
I've completed my first dumpcycle with my current config, and I'm
fairly certain that drive compression has been turned off the whole
time, but I'm not 100% sure. I now have in place a script that ensures
drive compression is off, but it was not put in place until a number of
runs had been done. I want to make sure all the tapes are uncompressed
before I reuse them.
My question: If I do a dd of some amount of data (like dumping the
first 32K of data as I would if I was saving the label), and then see
(via mt) that the drive's compression is still off, is it safe to
conclude that the tape was written with compression off?
I've read posts that indicate a compressed tape will silently set drive
compression back on, but will that change still be visible to mt?
BTW, the drive has no DIP switches for setting compression-- it is
completely controlled by software. Also, my system is Linux, so there
are no compression-related device names. I am relying strictly on mt
to manipulate the drive outside of AMANDA, so it's important that I be
able to trust its output.
Thanks,
Eric
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