TSM really likes to fill a storage pool tape before starting on
a new one, and sometimes this can result in contention.
For example, I had an Archiving user whose session was waiting
on a tape that was busy as input to a Backup Stgpool that would
be reading from that tape for some time.  To keep the user from
waiting further, I did an Update Volume ... Access=Readonly
which TSM immediately recognized to allow the archive session
to proceed with another output volume.  I then did
Update Volume ... Access=Readwrite to put the contended volume
back into its original state, and everyone was happy.
One of the various little tricks we TSM admins can perform.

   Richard Sims, BU