Kelly,
  I notice there hasn't been any feedback on your post. The reason may be
that there are few, if any, TSM on the mainframe installations. I ordered my
ADSM to TSM upgrade some time ago and haven't received anything yet. I think
the reason is that IBM forgot about marketing to the mainframes when they
moved their storage management product to Tivoli. It seems there is only one
person/business partner handling this in the USA.
  As for performance issues on the mainframe...  TCP/IP, OSA's (Open Systems
Adaptors), tape technology, and especially, shared CPU resources come to
mind.
  Sizing? Pretty much the same as sizing for any other platform.

John G. Talafous                         Sr. Tech. Prog/Anal
The Timken Company                 Phone: (330)-471-3390
P.O. Box 6927                           Fax  : (330)-471-4034
1835 Dueber Ave. S.W.
Canton, Ohio USA  44706-0927
talafous AT timken DOT com                  http://www.timken.com/