We have 2 3580 drives with the 3583 changer. The devclass for these drives 
shows them being of format=ultriumc, which I assume means compressed. I have 
compression turned on at the clients. Are my drives also compressing, or is 
there more to setting up drive compression than formatting with the ultriumc 
option? When my tapes are first checked in they show estimated capacity of 
about 200GB, once they are used and "full" they show an estimated capacity of 
about 100GB.

Also, is there a "best" way to compress, or does it differ depending on disk 
space, processor, backup window, etc.

Thanks in advance,

Jeff