Matt, 

Don't be so sure...  my MVS folks are telling me that there is no way TSM is 
over riding their micro-code hardware level compression.  (but I will double 
check with them and again as well as with
Tivoli).  

With regard to compressing data twice, I disagree.  There's something very 
wrong with it.  That's why it is strongly recommended not to do it. (not just 
with TSM, but with all data)  Some data that
goes thru multiple compression routines can "blow up" to 2x the size the file 
started out as.

And finally, the reason we turn compression on at the client, is to compress it 
before it rides our very slow network.  Otherwise, I wouldn't.  

Regards, Joe