This one also bit me a few months back. It turned out our hardware
environment was fine, but we had somehow (installation consultant) added a
"compression yes" command in all client options sets. (q cloptset) Thus, all
clients were compressing before sending data to the TSM server.

So, check this also. After adjusting, we have seen compression, in some
cases, approach 5:1 and usually exceed 3:1. We have 3590-E1A drives.

John G. Talafous              IS Technical Principal
The Timken Company            Global Software Support
P.O. Box 6927                 Data Management
1835 Dueber Ave. S.W.         Phone: (330)-471-3390
Canton, Ohio USA  44706-0927  Fax  : (330)-471-4034
talafous AT timken DOT com           http://www.timken.com