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.  You can use the optional gzip 
> compressor on portions of the system to much better advantage in 
> terms of achieved compression ratios, and generally can stuff more 
> data onto a tape than using the hardware compressor can do.  Here, 
> under what would be termed ideal conditions, I've had amanda email me 
> and rep[ort that it just put a bit over 12Gb on a 4Gb tape that has 
> the last 370megs reserved for something else I'm doing here.

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.

> >Estimated time to write 2 * 102400 Mbyte: 14400 sec = 4 h 0 min
> >wrote 3244032 32Kb blocks in 99 files in 7310 seconds (short write)
> >wrote 3244032 32Kb blocks in 198 files in 7666 seconds (short write)
> >define tapetype HP-C7971A {
> >    comment "just produced by tapetype prog (hardware compression
> > on)" length 101376 mbytes
> >    filemark 0 kbytes
> >    speed 13871 kps
> >}

-- 
Joshua Baker-LePain
Department of Biomedical Engineering
Duke University