Data Protection, Snapshots, and Replication
This domain tests protection policy design: how snapshot rules and replication rules combine, what snapshots actually consume, and where native replication and Metro volumes fit. Questions often hinge on the difference between RPO and retention.
Protection policies
- A protection policy is a reusable object containing a snapshot rule, a replication rule, or both. It is assigned to volumes, volume groups, and file systems.
- Snapshot rules define frequency and retention, for example every 15 minutes with 4-hour retention. Manual snapshots can be taken outside the schedule.
- Replication rules define the remote system, the RPO, and the retention of replicated snapshots. Native asynchronous replication works for block and file.
- Metro volumes provide synchronous active-active block access across two appliances for near-zero RPO; they are not a backup and do not replace snapshots.
Snapshot behaviour
PowerStore snapshots are redirect-on-write and space-efficient: there is no preallocated reserve per volume. Space is consumed as the source or snapshot data changes. Restoring a snapshot reverts the source; cloning creates an independent volume from the snapshot without affecting the source.
Worked example
An application needs 15-minute recovery points kept for four hours locally, plus a remote copy with a one-hour RPO. The protection policy uses a snapshot rule of every 15 minutes with 4-hour retention, and a replication rule with a 1-hour RPO. The local RPO is 15 minutes; the remote RPO is 1 hour; the 4-hour figure is retention, not RPO. Sizing must cover local snapshot growth and replicated snapshot space at the remote site.
Traps that cost marks
- Confusing RPO with retention, or quoting the snapshot interval as the remote RPO.
- Claiming snapshots reserve a fixed percentage of volume capacity.
- Treating Metro volumes or replication as a substitute for backup.
- Forgetting that a policy must be assigned; an unprotected volume has no snapshots just because a rule exists.