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Re: tapetype w/compression for a HP Ultrium LTO 1 drive
2006-03-17 12:20:48
On Fri, 17 Mar 2006 at 12:00pm, Salada, Duncan S (Titan) @ TITAN wrote
Something with no line breaks in the paragraphs. Please add some line
breaks.
I'm having trouble getting amtapetype to give me a 200gb tapetype for a
HP Ultrium LTO 1 drive. It tells me that hardware compression is on,
and I've tried using "-e200g" with "-f/dev/rmt/0ubn" and
"-f/dev/rmt/0cbn" in desperation. But it still will only give me the
100gb tapetype:
amtapetype writes random data, which does *not* compress. In days of
yore, you'd get a smaller than expected tapelength if you wrote to a drive
with compression on, because the data would actually expand when going
through the hardware compressor. LTO drives are smart enough to know when
data won't compress, and don't try to compress such data. Thus, your
100gb tapelength.
To use hardware compression with amanda, you essentially lie to amanda.
Estimate how compressible your data is, and increase the tapelength from
the native size by that amount. If you think your data really will
compress to 50% it's original size, then set your tapelength to 200GB.
--
Joshua Baker-LePain
Department of Biomedical Engineering
Duke University
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