Mainframe Enablers TimeFinder SnapVX and zDP 8.5 Product Guide

The LINK action associates a created and activated snapshot with a target device. Once link processing is complete, the device can be accessed.

The target device for the LINK command may be the original source device, which logically would simulate a restore operation, or any other compatible device with the same or larger number of cylinders.

Any previous tracks assigned to the target device are returned to the pool. If a snapshot is linked more than once to the same target device, only the differences are applied.

Targets can be linked in COPY mode to create full-copy clones. If an application is to find a particular point-in-time copy among a large set of snapshots, SnapVX enables you to link and relink until the correct snapshot is located.

If the linked target is in NOCOPY mode, a cascading snapshot is a dependent snapshot. A target device cannot be unlinked without removing dependent snapshots. Or, the snapshots should be removed in the reverse order of creation.

After an UNLINK, any copied tracks remain on the device. The target device may be in one of the following states:

• If LINK with MODE(COPY) was specified, and the copy is complete, the data is whole.
• If LINK with MODE(COPY) was specified, and the copy is not complete, the device is in an unpredictable state.
• If LINK with MODE(NOCOPY) was specified, the data on the target is retained.

The state of the data on the target device after an UNLINK is also dependent on whether the track definition process is complete on the target device. For example, if LINK with MODE(NOCOPY) was specified but the UNLINK was run without waiting for the track definition process to complete, the target device data would be in an unpredictable state.

Linking to target R1s with NOCOPY mode

Starting with PowerMaxOS 5978.600, you can link snapshots to target R1 devices using the MODE(NOCOPY) setting.

The LINK operation is considered complete only when all target R1 invalid tracks are cleared. Before finishing the job, SnapVX checks for R1 invalid tracks on the target device. If invalid tracks are detected, messages are issued to indicate the count of invalid tracks and the storage system and device where they were found. For all target R1 devices, SnapVX waits for the target to be defined and for the SRDF invalid tracks to be synchronized to the R2 before the job completes.

One of the following parameters must be set to YES to allow for linking to target R1s with MODE(NOCOPY) when using SRDF/S or SRDF/A:

• For SRDF/S: SRDFS_R1_target
• For SRDF/A: SRDFA_R1_target

Impact of linking on SRP usage and SRDF data transfer

• An initial link is a LINK command that is issued between a source and a target device that do not have an existing LINK relationship.
• A logical relink is a LINK command that is issued between a source and a target device with an existing LINK relationship.
• A logical restore is a LINK command where the source and target are the same device.