Because an unauthorized user cannot modify a VTOC, neither the VTOC nor the VTOC index need be recovered from an error caused by an unauthorized user.

A system error can affect a VTOC and VTOC index by interrupting DADSM while it is updating, leaving the VTOC or the VTOC index (or both) in a partially-updated state. Both the VTOC and the VTOC index allow DADSM to recover from such an interruption.

For a nonindexed VTOC (or a VTOC with an index that has been disabled), a subsequent call to DADSM create or extend, causes VTOC convert routines to reestablish the free space DSCB chain.

For an indexed VTOC, a subsequent call to any DADSM function causes the recovery of the previous interrupt (either by backing out or completing the interrupted function).