The TSM  5.1 base code,  first PTF and patch 5.1.1.1 are affected by APAR PQ63371. 
This APAR only affects the MVS, OS/390 and z/OS customers.
Customers affected are those with 3590 tape drives who are writing to
short block tapes.  TSM 4.1 and below customers and TSM 4.2 and above
customers running under OS/390 2.09 or below create short block tapes. 
Customers  who are either migrating to TSM 5.1 from TSM 4.1 or below
running OS/390  2.10 and above, customers running TSM 5.1 on OS/390 2.09 
or below and upgrading to OS/390 2.10 or above,or customers who have
recently migrated from TSM 4.1 or below, or OS/390 2.09 or below are
most likely to be affected.
All TSM  customers should apply the zap in the APAR if the migration 
or upgrade is already in production, or should apply the 5.1.1.2 patch
or wait for the PTF containing the fix for the APAR before going into production.
See APAR PQ63371 for more details on the problem.
Thank you,
Tivoli Storage Manager  Development