Dell PowerVault ME4 Series Storage System Administrator’s Guide

Snapshot creation and levels

Creating snapshots is a fast and efficient process that merely consists of pointing to the same data to which the source volume or snapshot points. Since snapshots reference volumes, they take up no space unless they or the source volume or source snapshot is modified.

Space does not have to be reserved for snapshots because all space in the pool is available for them. It is easy to take snapshots of snapshots and use them in the same way that you would use any volume. Since snapshots have the same structure as volumes, the system treats them the same way.

Because a snapshot can be the source of other snapshots, a single virtual volume can be the progenitor of many levels of snapshots. Originating from an original base volume, the levels of snapshots create a snapshot tree that can include up to 254 snapshots, each of which can also be thought of as a leaf of the tree. When snapshots in the tree are the source of additional snapshots, they create a new branch of the snapshot tree and are considered the parent snapshot of the child snapshots, which are the leaves of the branch.

The tree can contain snapshots that are identical to the volume or have content that has been later modified. Once the 254-snapshot limit has been reached, you cannot create additional snapshots of any item in the tree until you manually delete existing snapshots from the tree. You can only delete snapshots that do not have any child snapshots.

You cannot expand the base volume of a snapshot tree or any snapshots in the tree.