Tapetype when utilizing hardware compression

[Don Potter]

I ran the tapetype test to our tapedrive (ADIC DS9400D) using DLTTAPE IV.  I frontpaneled the compression so I expected at least 40 GB when the tapetype was completed.  But I only got about 17GB:

Command: tapetype -d /dev/rmt/0n

define tapetype unknown-tapetype {
    comment "just produced by tapetype program"
    length 17587 mbytes
    filemark 13 kbytes
    speed 1011 kps
}

Then I ran it with software compression (/dev/rmt/0cn) and I only got 20 GB:

Command:   tapetype -d /dev/rmt/0cn

define tapetype unknown-tapetype {
    comment "just produced by tapetype program"
    length 19565 mbytes
    filemark 4 kbytes
    speed 1101 kps
}

Both ways I would of expected close to double the native writes.  Any ideas why the compression would not of increased.

Any suggestions would be appreciated.

Don Potter