On Wed, 7 Jan 2009, Chris Hoogendyk wrote:

> Most backup software leaves the responsibility for planning more in the
> sysadmin's hands. If the software is just writing data to the tape until
> it hits the end of tape and then asking for another, hardware
> compression is a logical choice.

Part of the preference for no hardware compression in Amanda and other
packages is that a lot of them assume fixed tape sizes, so the only
thing that hardware compression gets you is less time to write to that
maximum.

ie: Program assumes tape is 33Gb. When 33Gb is reached the program
demands the tape be changed, even if the tape is only physically half
used thanks to hardware compression

Most of these types of programs have an all-or-nothing approach to
restores. This is not exactly the bacula model.

Even with hardware compression switched off, spooling is likely required
to prevent shoeshining of modern tape drives. Spooling hardware MUST be
fast enough to keep up. Switching on hardware compression increases those
requirements but the budgetary increase is minor.





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