On Thu, Jul 08, 2004 at 08:50:17AM -0400, Joshua Baker-LePain wrote:
> On Thu, 8 Jul 2004 at 8:35am, Gene Heskett wrote
> 
> > On Thursday 08 July 2004 01:32, Alexey I. Froloff wrote:
> > >* Alexey I. Froloff <raorn@> [040707 14:10]:
> > >> P.S. Right now I figured how to turn HW compression off (with mt
> > >> utility) and started amtapetype again...
> > >
> > >Thanks to all for your help.  amtapetype finished successfully.
> > >
> > >$ /usr/sbin/amtapetype -e 100g -f /dev/nst0 -t "HP-C7971A"
> > >Writing 1024 Mbyte   compresseable data:  25 sec
> > >Writing 1024 Mbyte uncompresseable data:  72 sec
> > >WARNING: Tape drive has hardware compression enabled
> > 
> > Please disable this as it hides the true tapesize from amtapetype AND 
> > amanda.  amanda can do a much better job of filling up a tape if 
> > amanda knows how much a tape can hold.
...
> 
> Actually Gene, for this drive disabling hardware compression isn't 
> necessary.  It's an LTO/Ultrium drive, and those are actually smart enough 
> to not compress already compressed data.  Notice (below) how he still gets 
> the full 100GB native capacity?  With those drives, you get the best of 
> both worlds -- you can mix software and hardware compression.  Very, very 
> slick.
> 

Gene's second point is still valid though.
What is the actual "real world data" capacity of the tape?
Amanda will think 100GB and yet the HW compressor will be
shrinking that 0-80% depending on the data compressability.
So running tapetype if you plan to use HW compression is
basically a time-waster as you will be guess-timating the
actual data capacity anyway.

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