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Dell PowerFlex 4.5.x Technical Overview

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Snapshots

PowerFlex enables you to create snapshots, that is, instantaneous copies of volumes. A snapshot can be manipulated as any volume exposed by the storage system. Snapshots that are taken simultaneously form a consistency group and can be manipulated as a group.

The PowerFlex storage system enables you to take snapshots of existing volumes, up to 128 per volume. The snapshots are thin provisioned and are extremely quick. For more information about thin provisioning, see "SAN virtualization layer."

Once a snapshot is generated, it becomes a new, unmapped volume in the system. You can manipulate it in the same manner as any other volume exposed by the PowerFlex storage system.

Figure 1. Snapshot operations

Snapshot operations

The structure related to all the snapshots resulting from one volume is referred to as a vTree (short for volume tree). When taking a snapshot in the system, you can specify more than one volume. All snapshots that are taken together form a consistency group. They are consistent in the sense that they were all taken simultaneously. So if there is a contextual relationship between the data that is contained by all the snapshot members, then that set is meaningful. The consistency group allows manipulation of the entire set.

If you remove an entire consistency group, all snapshots that were taken together are removed. In RED, S211 is a snapshot of V2. Since S112 and S211 were taken together, they compose a consistency group that is designated as C1.

NOTE:
  • The consistency group is only for convenience purposes. There are no protection measures done by PowerFlex to conserve the consistency group. For example, you can remove a snapshot that is a member of a consistency group.
  • Support of removal of a parent snapshot in the system. You can merge the parent to a child snapshot.
  • It is recommended not to trim volumes that contain snapshots as the logical capacity may not shrink.

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