On Tue, Mar 14, 2006 at 01:23:17PM -0500, Carl Holzhauer wrote:
> Just wanted to post this incase some one else has the same backup
> device.
>  
> Backup device is a Comapq Storage Works SSL2020
> Tapes are Compaq AIT 50GB
> amtapetype returns the following:
> 
> define tapetype unknown-tapetype {
>     comment "just produced by tapetype prog (hardware compression on)"
>     length 43605 mbytes
>     filemark 0 kbytes
>     speed 5583 kps
> }

The typical 15% loss of native capacity when random data is
fed through the tape drive's compressor due to its expansion
of the random data rather than compression.

If you plan to use this drive with the compressor on you should
not ALSO use software compression.  The tapes capacity for gzipped
data would be closer to 50GB without the compressor.  You would
need another amtapetype run without HW compression to check the
actual capacity.

If, OTOH, you don't plan to gzip (SW compression) your amanda
dumps and plan to let the drive's compressor do the job, then
the above tapetype is meaningless.  Depending on the compress-
ability of your data, it could be anywhere from 50 to 150GB.
It will be just a guesstimate.  If amanda keeps filling your
tapes, lower your guess.


-- 
Jon H. LaBadie                  jon AT jgcomp DOT com
 JG Computing
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