Mainframe Enablers TimeFinder SnapVX and zDP 8.5 Product Guide

With PowerMaxOS 5978 and earlier, upon a LINK operation, the operating environment unconditionally and automatically starts a background define process.

The LINK operation updates the target track pointer table to point directly to the track data instead of having to access the track using the snapshot. When an UNLINK operation occurs, the target continues to indicate any tracks that have been defined or written to. When a snapshot is terminated, tracks that are still pointed to as a result of a previous LINK and background define operation to a target device, or written to on the target device, are not freed. These tracks continue to consume space.

The FREE operation clears the in-memory track pointers of a device. After the tracks that were linked to a device are freed, the device is no longer able to access the snapshot data that it was linked to.

If the target device of the FREE operation is the last device or snapshot sharing these tracks, they are returned to the free track list in the storage resource pool. The space is freed up for future allocations.

Tracks that are allocated for snapshots and devices are only freed when no device or snapshot is sharing them. A snapshot unshares tracks only when it is terminated. Multiple snapshots can share track allocations. All snapshots sharing a track must be terminated (and no other source or target devices must be sharing the track) before the track is returned to its pool and the space that is freed up and ready for reallocation.

The requirements and restrictions are as follows:

• Freeing an SRDF device or a device with any session is blocked.
  NOTE:To list sessions for a device, use the QUERY VOLUME command that is described in the TimeFinder/Clone Mainframe Snap Facility Product Guide.
• You cannot free a device that has Thin Reclaim active.
  NOTE:To verify the 04xx TRU session, use the TRU,DISPLAY,DEVICE command that is described in the ResourcePak Base for z/OS Product Guide.
• If the target device is online to the current host, the FREE operation is blocked. If the target device is online to some other host, the FREE operation is only blocked when the CHECKONLINEPATHSTATUS parameter is set to YES.

To view the count of tracks that are to be freed up in SRP space, issue the QUERY FREE command.

To free tracks, use either of the following:

• The FREE command
• The FREE parameter available on the GLOBAL, UNLINK, and TERMINATE command
• The &FREEUNLK site option