Jon LaBadie wrote:

On Wed, Oct 26, 2005 at 04:33:19PM -0700, Alan Jedlow wrote:

Hi,

I know the "docs" say to turn hardware compression
off before running amtapetype, unfortunately I've
found no info on how to disable hw compression on a
Dell PowerVault 122T LTO2 library.

How "bad" is this result ?

-----------------------------------------------------------------------
-bash-3.00$ /usr/sbin/amtapetype -e 200g -f /dev/nst0 -t Ultrium2
Writing 4096 Mbyte   compresseable data:  40 sec
Writing 4096 Mbyte uncompresseable data:  350 sec
WARNING: Tape drive has hardware compression enabled
Estimated time to write 2 * 204800 Mbyte: 35000 sec = 9 h 43 min
wrote 6422528 32Kb blocks in 98 files in 6420 seconds (short write)
wrote 6422528 32Kb blocks in 196 files in 6719 seconds (short write)
define tapetype Ultrium2 {
  comment "just produced by tapetype prog (hardware compression on)"
  length 200704 mbytes
  filemark 0 kbytes
  speed 31300 kps
}
-----------------------------------------------------------------------

Most drives use a compression algorithm that expands,
rather than compressing, data that is random or nearly so.

LTO drives have the nearly unique feature for dealing with
this problem in that they sense the expansion potential and
turn off compression themselves.

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Toomas Aas --------------------------------------------------------
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