On Fri, Jul 07, 2006 at 01:57:48AM -0700, Joe Donner (sent by Nabble.com) wrote:
> 
> I got these replies by email, which I think clear it up for me.  Still not
> sure about whether I can start from scratch by erasing the existing
> hardware-compressed tapes, and then issuing mt -f /dev/nst0 defcompression 0
> in crontab, but I'm going to try anyway:
> 
> Software compression is normally recommended when using amanda as it allows
> amanda to better estimate how much will fit on a tape. It's also produces
> smaller archives - usually. To turn on and off varies for mt implemention,
> but if that's what your manpage says. Also is best to either use it or not.

===========
> If you switch over you need to physically label the tape etc otherwise
> restores won't be able to read the tape if you got the setting wrong to the
> tape...

This part is not accurate.  Tape drives automatically adjust to the HW
compression or not during reads.  All the settings we have been talking
about "defcompression", "stinit", ... affect writing, not reading.

Where you might have a problem is if you made a tape with SW compressed
(gzip'ped) dumps, then changed your config to use HW only, then you would
have to manually recover the data, insert the gzip command, or temporarily
reset your config during recovery.  The data are still valid and recoverable.


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