Dell Solutions Enabler 10.0.0 TimeFinder SnapVX CLI User Guide

The target device of a snapshot can be used as the source device for additional snapshots.

The figure below shows Snapshot B cascading off of the target of Snapshot A, where the target of Snapshot A is the source for Snapshot B.

There are no architectural restrictions on the number of cascading hops, and multiple targets can be linked from any of the snapshots.

If the linked target is in NoCopy mode, the cascading snapshot is considered a dependent snapshot. Target devices cannot be unlinked without removing dependent snapshots (in the reverse order of their creation). However, the copy mode is changed to Copy the target can be unlinked once link is fully copied.

A relink operation to a target with dependent snapshot is allowed, but if the relink is in NoCopy mode, the unlink is allowed only if there are no new snapshots off of that target device.

For HYPERMAX OS, a linked target must be fully defined before you can create snapshots off of it. When a target is first linked, all of the tracks are undefined. At this point the target does not know where in the SRP the track is located, and host access to the target must be derived from the SnapVX metadata. A background process eventually defines the tracks and updates the thin device to point directly to the track location in the source device's SRP. For PowerMaxOS, creating a snapshot off the link target if the link is not defined, or when restore is in progress and not defined yet is allowed, however these snapshots can only be used once they are fully defined.