> -----Original Message-----
> On Thursday 19 June 2003 11:51, Ean Kingston wrote:
> >I couldn't find this one in the list archives, so here it is.
> >
> >I'm using 40GB DLT tapes (according to the label). Despite what the
> > comment produced says, I used the non-compressed device. I didn't
> > give it an estimate for the tapesize.
> >
> >Writing 256 Mbyte   compresseable data:  34 sec
> >Writing 256 Mbyte uncompresseable data:  105 sec
> >WARNING: Tape drive has hardware compression enabled
> >Estimated time to write 2 * 1024 Mbyte: 840 sec = 0 h 14 min
> >wrote 1102644 32Kb blocks in 3372 files in 21817 seconds (short
> > write) wrote 1101228 32Kb blocks in 6756 files in 29828 seconds
> > (short write) define tapetype HP-DLT1e {
> >    comment "just produced by tapetype prog (hardware compression
> > on)" length 34499 mbytes
> >    filemark 13 kbytes
> >    speed 1399 kps
> >}
> 
> And it appears the hardware compressor being on cost you 5.5 gigs.
> The various 'tapetype' programs all use the output of /dev/urandom as 
> the data source, and the output of /dev/urandom is not compressible, 
> and will in fact grow by about the percentage you see above in being 
> passed thru the hardware compressor.
> 
> As others have noted Ean, you can turn it off, but this must be done 
> for every new tape that's inserted as the recognition phase of the 
> drive will turn it back on when the tapes are changed.  Such info as 
> how to turn it on/off should be on the drive makers web page.  To 
> your vendor its obviously not a very high priority to obtain that 
> info for you else he would have fired up a browser and found it on 
> the spot.

I'm using Solaris and, according to the documentation, it should not be using 
hardware compression unless I specify the 'compress' device (/dev/rmt/0cn) as 
opposed to the one I did use (/dev/rmt/0n). If what you say it true there is 
some way to force HW compression for the tape drive regardless of what the OS 
wants.