On Fri, May 23, 2003 at 10:02:49PM +0800, Mathias Körber wrote:
> The first tapetype below I measured today (with a 150m tape)on a new
> DELL PowerVault 100T DDS4 tapedrive (Archive Python 06408-XXX)
> with hardware compression turned off (dip switch 1->OFF).
> Maybe it will come in handy for someone else..
> Note I lowered the capacity to have some buffer. Edit at your
> own preference..
> 
> define tapetype PV-100T-DDS4-150M {
>     comment "produced by tapetype on adelphi , no hw compression"
>     # measured: length 19457 mbytes
>     # leave some for tolerances...
>     length 19000 mbytes
>     filemark 32 kbytes
>     speed 2686 kps
> }
> 
> This one I found somewhere on the net:
> I would be interested in possible reasons for the
> 3GB difference in capacity (and the marked diff in
> filemark sizes!).
> The speed may be due to SCSI configuration
> (other controller, more devices on the same bus etc)
> 
> define tapetype PV-100T-DDS4 {
>         comment " Dell PowerVault 100T DDS4, from 
> http://amanda.sourceforge.net/fom-serve/cache/188.html";
>         length 16534 mbytes
>         filemark 0 kbytes
>         speed 2278 kps
> }

As Joshua already noted, certainly this was done with HW compression.
A 15% lowerer than expected value is always the red flag.

As to the filemark difference, that means between the two passes made
during your run there was a difference in total capacity of 3.2MB.
The second pass wrote about 100 extra files (and file marks) so 3.2MB/100
is your 32K mark.  3.2MB out of 19457MB.  Maybe the temperature raised
a bit and the tape streched 1mm :)

-- 
Jon H. LaBadie                  jon AT jgcomp DOT com
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