Using SnapShot copy, PPRC, and RVA together

The RAMAC Virtual Array (RVA) storage subsystem provides the unique ability to combine SnapShot copy functions with PPRC functions. For instance, you can use PPRC to migrate data to a different RVA subsystem; you can end the pairs and use SnapShot copy at the secondary subsystem. This ability can be very beneficial for data mining applications. However, there are some operational considerations regarding the interaction of SnapShot copy with volumes that are part of a PPRC pair.

• You cannot snap (copy) data onto any volume that is part of a PPRC pair. A primary volume cannot be the target of a SnapShot copy command even if it is in a suspended state.
• The primary device can be the source for a snap without having to change the state of the primary volume.
• SnapShot copy requires that space be available on the same RVA subsystem where the source of a snap resides. If you plan to use a SnapShot copy on an RVA subsystem that already has PPRC pairs, then provide volumes on that subsystem that are not part of a PPRC pair. You cannot, therefore, assign all of the volumes in a subsystem to be part of PPRC pairs and still use SnapShot copy on that subsystem.
• If you plan to use SnapShot copy at the secondary RVA subsystem, ensure that space is available at that subsystem. This real space must be independent of PPRC pairs. You cannot, therefore, have all 256 volumes as part of PPRC pairs.
• Do not put PPRC volumes into a SnapShot target storage group. Also, do not include a volume that is part of a PPRC pair within a SnapShot volume list. SnapShot does not check PPRC status. The SnapShot copy operation will fail if you attempt to allocate any part of a data set to a volume that is part of a PPRC pair. SnapShot copy uses all volumes available to it on a space-available basis when it dynamically allocates space for the target copy.
• You cannot perform any read or write I/O to a secondary volume of a PPRC pair. However, you can snap copies of data from the secondary device and bring the PPRC pairs back to active status. The following procedure outlines a quick way to do this:
  1. Suspend the pair.
  2. Recover the secondary, returning it to simplex.
  3. Snap the secondary.
  4. Issue a CESTPAIR command with the RESYNC parameter to copy only the changes.

  You can use a similar procedure in conjunction with the CGROUP command (MVS TSO command only) to snap data from secondary devices that contain related information.

  1. Issue a CGROUP command with FREEZE to suspend all pairs on the path between a primary logical storage subsystem and a secondary logical storage subsystem.
  2. Recover the secondary volumes, returning them to simplex.
  3. Snap the secondary volumes.
  4. Issue a CESTPAIR command with the RESYNC parameter to copy only the changed tracks of each volume.