You may be running into the Filling problem, as described in ADSM QuickFacts. Your KEEPMP and MOUNTRetention values may cause TSM to dismount the recently written volume. But if a volume is dismounting, TSM will shrug its shoulders and call for a scratch to be mounted - ostensibly because it's faster than waiting for a full dismount-store-retrieve-remount tape sequence.
Richard Sims
