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Dell EMC PowerMax and VMAX All Flash: TimeFinder SnapVX Local Replication
Executive summary Introduction TimeFinder SnapVX overview
Creating snapshots
Generation numbers
Time-to-live value
Host writes to source
Redirect-on-write
Replication cache
Shared allocations
Linking target volumes to snapshots
Relinking
Unlinking
Defining state
Linking a larger target
Source-volume or linked-target SRP relationships
Restore operations
Cascading snapshots
Reserved capacity
Interoperability
Storage group operations
Secure snaps
Online device expansion
Role Based Access Controls
Implementing TimeFinder SnapVX PowerMaxOS Q3 2020 release enhancements TimeFinder legacy modes: Mirror, Clone, and VP Snap Conclusion Appendix A: TimeFinder SnapVX state table Appendix B: Geometry compatibility mode Appendix C: Monitoring the copy process Appendix D: Nocopy Linked Target behavior before HYPERMAX OS 5977.810.184 Appendix E: Scheduling snapshots with Unisphere for PowerMax Appendix F: System resource planning for capacity and performance Appendix G: Technical support and resources

Host writes to source

Home > Storage > PowerMax and VMAX > Data Protection > Dell EMC PowerMax and VMAX All Flash: TimeFinder SnapVX Local Replication > Host writes to source

Host writes to source

  • Host writes to source volumes create snapshot deltas in the SRP. Snapshot deltas are the original point-in-time version of each track that has been updated since a snapshot was established. Multiple snapshots can share a single snapshot delta if all are active at the time a source track was updated. So, if a source track that is being updated needs to be preserved by multiple snapshots, only one snapshot delta is needed. This sharing allows the snapshots to be as space efficient as possible.

    The output of command symsnapvx list –detail and other commands report the number of deltas for each snapshot. The symsnapvx list –detail output also has a “Non-Shared Tracks” field that provides the number of tracks uniquely allocated to each snapshot. This information is valuable because it can be used to determine which snapshots are using the most non-shared space and are most beneficial to terminate in the event of needing to free some space in the SRP. Only non-shared space is freed from the SRP when a snapshot is terminated.