One day we have found the some kind of "Turbo button".
We have 2 types of media servers (HP & SUN) and IBM 3584 LTO-2 library.
We are using native ibm drivers (atdd) on HP and standart st driver on
SUN.
After cold reset of library we have only 35MB/s per drive (i.e. backup
without compression) until we use the HP backup.
After first HP using, performance of any (SUN or HP) SAN backup is up to
75 MB/s.
Seems native driver sends the SCSI command, that turn on compression on
library, but Solaris st - driver can not do it. 
 
Sergey
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