On 14/01/11, Jose Antonio Rodriguez Martin (jarodriguez AT cgi DOT es) wrote:
> I tried it and no longer works. I see that when I run:
>   # mt-f / dev/nst0 compression 1
> compression is enabled:
> # tapeinfo-f / dev/sg5
> ...
> DataCompEnabled: yes
> ...
> 
> But by launching the copy tape is uncompressed ...
> Do not let the copy over 400 GB (800 GB compressed).

The tape device will attempt to compress the data. It will write to tape
either the compressed data or the original depending on which is the
smaller. Compressability is a function of the compression implementation
and the data being provided to the tape system. Some data can grow in
size after attempting to compress it.

It is difficult to know how well any particular data will compress. We
achieve about 30% compression on our LTO4 tape drive system using
hardware compression.

-- 
Rory Campbell-Lange
rory AT campbell-lange DOT net

Campbell-Lange Workshop
www.campbell-lange.net
0207 6311 555
3 Tottenham Street London W1T 2AF
Registered in England No. 04551928

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