The two DFSMShsm PDA data sets are called the ARCPDOY data set and the ARCPDOX data set.
DFSMShsm always writes information in the ARCPDOX data set. When the ARCPDOX data set becomes full, DFSMShsm automatically swaps the two PDA data sets. You can use the SWAPLOG command to swap the two PDA data sets.
The z/OS DFSMShsm Diagnosis contains additional information about the PDA facility.