Something I found on a forum is quite a good howto:
You have to format a volume (really just a file) that is a certain size
you feel is adequate to reduce the utilization of the DB. You should
run the TSM command Q DBV F=D and look at the size of the other volumes and their location to get and idea for sizing. Then run the dsmfmt command from the UNIX shell (it’s not a tsm internal command). Also make sure that the volume you create is divisble by 4MB with a remainder of 1MB
otherwise you can waste some space. The reason for this is that TSM has
its own logical volume manager and it looks at the DB volumes as LV’s
and the 1MB is for management of the logical blocks within the volume
(if you run a SHOW LVM you’ll see what I mean). Here is an example of the dsmfmt command Note: all info between <> is examples.
dsmfmt -db </tsmdb/db03.dsm> <5121>
Once the volume is defined go into TSM and issue the
DEFINE DBV </tsmdb/db03.dsm>
Then issue a Q DB and you’ll see the volume was added to your DB size but is not in use (Look at the Available Space vs. the Assigned Capacity). To use the space you issue the
EXTEND DB <MB AMOUNT>
The amount should be divisble by 4MB since TSM allocates internal blocks within the volume 4MB at a time. Now run a Q DB again and you should see the difference.
Thanks to chad_small from adsm.org
original post: http://adsm.org/forum/showthread.php?t=11524