On Tue, Sep 06, 2005 at 05:09:56PM +0100, Rodrigo Ventura wrote:
> 
> Another quick question: hitting end-of-tape error does not mean that
> the tape length setting in tapetype is wrong?
> 
> I have:
> 
> define tapetype HP-DAT-72x6 {
>     comment "HP autoloader DAT 72x6"
>     # data provided by Rodrigo Ventura <yoda AT isr.ist.utl DOT pt>
>     length 31255 mbytes
>     filemark 527 kbytes
>     speed 1580 kps
> }
> 
> (got it from running an amanda utility to detect it by writting
> garbage to tape)
> 

You had hardware compression on when you ran amtapetype.
Random data is expanded by the tape drives 'compression'
algorithm.  So the apparent capacity is lower than
expected by 5 - 15%.  Allowing for marketing hype,
I'd expect your 36GB tape to measure about 35-35.5 GB.
Your 31.3GB is about 12% low, thus my statement about
hardware compression being on.

See the oft appearing discussions and docs about HW vs SW
compression, about setting compression for your particular OS,
and about how, for some OSs you may have to "reformat" your
tapes to not use HW compression should you prefer not to.

BTW the ability to control compression on HP DDS drives may
involve some DIP switch settings, some pretty well hidden.
If set some ways, the drive is locked to one setting or
another and software can't control it.

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