In TSM v6 the “dsmfmt” is no more available, then you need to go into TSM admin console to format new DISK volumes.

You can format multiples volumes in one operation, TSM add an ID at the end of the name, and existing volumes won't be deleted.

tsm: SERVER1>def vol backuppool /tsm/tsmstgpool1/backupstg format=2000 wait=yes number=2
ANR0984I Process 1 for DEFINE VOLUME started in the FOREGROUND at 10:46:45.
ANR2206I Volume /tsm/tsmstgpool1/backupstg000 defined in storage pool BACKUPPOOL (device class DISK).
ANR0986I Process 1 for DEFINE VOLUME running in the FOREGROUND processed 1 items for a total of 2,097,152,000 bytes with a completion state of SUCCESS at 10:46:54.
ANR0984I Process 2 for DEFINE VOLUME started in the FOREGROUND at 10:46:54.
ANR2206I Volume /tsm/tsmstgpool1/backupstg001 defined in storage pool BACKUPPOOL (device class DISK).
ANR0986I Process 2 for DEFINE VOLUME running in the FOREGROUND processed 1 items for a total of 2,097,152,000 bytes with a completion state of SUCCESS at 10:47:02.

tsm: SERVER1>def vol backuppool /tsm/tsmstgpool1/backupstg format=2000 wait=yes number=2
ANR0984I Process 3 for DEFINE VOLUME started in the FOREGROUND at 10:47:22.
ANR2206I Volume /tsm/tsmstgpool1/backupstg002 defined in storage pool BACKUPPOOL (device class DISK).
ANR0986I Process 3 for DEFINE VOLUME running in the FOREGROUND processed 1 items for a total of 2,097,152,000 bytes with a completion state of SUCCESS at 10:47:31.
ANR0984I Process 4 for DEFINE VOLUME started in the FOREGROUND at 10:47:31.
ANR2206I Volume /tsm/tsmstgpool1/backupstg003 defined in storage pool BACKUPPOOL (device class DISK).
ANR0986I Process 4 for DEFINE VOLUME running in the FOREGROUND processed 1 items for a total of 2,097,152,000 bytes with a completion state of SUCCESS at 10:47:40.