I noticed that my tape drive (HP DAT autoloader) requires a "mt
compression 0" prior to tape access. It seems that even after reading
the tape label in a non-compressed tape, when it writes, it uses
hardware compression. I noticed it comparing the tapeer data transfer
rates in several amdumps after "mt compression 0", and right after
power cycling the server and the tape drive: approx 3000KB/s w/
non-compression, and approx 2500KB/s w/ compression.

I thought about running "mt compression 0" before each amdump (in a
single script, via crontab), but my system rejects the mt command when
no tape is loaded:

$ mt compression 0
/dev/tape: Input/output error

But after a "amtape ... slot current", the mt compression command runs
fine.

Is it possible to issue the mt command after amdump doing an amtape,
but before actually dumping?

Maybe I could to a "amtape ... slot current/next/?" before the
amdump. What argument after "slot" shall I use to maximize the
probability of amdump finding already in the slot the desired tape?

Cheers,

Rodrigo

-- 

*** Rodrigo Martins de Matos Ventura <yoda AT isr.ist.utl DOT pt>
***  Web page: http://www.isr.ist.utl.pt/~yoda
***   Teaching Assistant and PhD Student at ISR:
***    Instituto de Sistemas e Robotica, Polo de Lisboa
***     Instituto Superior Tecnico, Lisboa, PORTUGAL
*** PGP fingerprint = 0119 AD13 9EEE 264A 3F10  31D3 89B3 C6C4 60C6 4585