On Sat, Feb 04, 2006 at 07:03:07PM +0100, uwe.kaufmann AT infoconsult DOT nu 
wrote:
> 
> Matthias Andree gave me some good advice here to use some linux scsi tools
> to circumvent the error message of "mt", which could not write the mode page
> (datcompression off).
> 
> As I wrote, I was able to change the compression using the sginfo command
> (see my posting some days ago)... but ...
> 
> But afterwards I started the amtapetype to extract the drive capacity
> information and please have a look what it reported:
> 
> Estimate phase 1...
> Writing 8 Mbyte   compresseable data:  708 sec
> Estimate phase 2...
> Writing 8 Mbyte uncompresseable data:  710 sec
> Estimated time to write 2 * 20480 Mbyte: 3635200 sec = 1009 h 46 min
> 
> Man, 1009 hours :-( I think that by changing the mode page I slowed down the
> drive dramatically.
> 
> [Quote] If amtapetype really runs for 9 days, you can be pretty sure there
> is something wrong with your approach.[/quote] from:
> http://www.amanda.org/docs/topten.html#id2552780

Good advice in that quote :))

Did you give amtapetype a good estimate of your tape size?

Might you have somehow mucked with the tape's blocksize when
you turned off compression?  Typically amanda uses 32KB blocks
and the drive is set to that or to "variable".  Some see much
better performance on newer drives with a larger blocksize.
Recent amanda versions allow this to be specified in amanda.conf.

> I still have a backup on the holding disk and some hours ago I started the
> flush to the tape, which should take 3-4 hours for 20g usually. I will see
> if it is still running tomorrow. If I do not find a solution I will have to
> restore the manufacturer settings with 'compr. on' again.

Not to start a 'holy war' about software or hardware compression,
but there is nothing wrong with deciding to go with HW compression.
Amanda can't do bookkeeping so well then and you have to guesstimate
the expected compression when specifying tape length.

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