Your Browser is Out of Date

Nytro.ai uses technology that works best in other browsers.
For a full experience use one of the browsers below
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

Generation numbers

Home > Storage > PowerMax and VMAX > Data Protection > Dell EMC PowerMax and VMAX All Flash: TimeFinder SnapVX Local Replication > Generation numbers

Generation numbers

  • It is possible to have multiple snapshots with the same name for the same set of source volumes, and generation numbers identify the different snapshots. It is important to understand how generation numbers are applied when deciding to either reuse snapshot names or to use unique names for each snapshot. Generation numbers are relative to existing snapshots at the time of creating or displaying snapshots, and they change as snapshots are created and terminated.

    When a snapshot name is reused, the new session becomes Generation 0 and all previous sessions with the same name have their generation numbers incremented by one. Similarly, if a more recent snapshot is terminated, all older snapshots have their generation numbers decreased by one. The most recent snapshot always has a generation number of 0. This is advantageous because after creating a new snapshot, the user knows that it is Generation 0 and does not have to search for the specific snapshot.

    For example, if a user creates a snapshot called hourly_backup at 1PM, the snapshot will be Generation 0. Then at 2PM they create another snapshot and reuse the name hourly_backup. At this point, the 1PM snapshot will become Generation 1 and the 2PM snapshot will be Generation 0. Similarly, at this point if the 2PM snapshot (Generation 0) was terminated, the 1PM snapshot will again become Generation 0.

    Reusing snapshot names and employing generation numbers can be very useful. A user could maintain a set number of generations for a specific snapshot. Each day the user creates a new snapshot and terminates the oldest, using the same commands each day. This makes scripting simple.

    However, the user must recognize that the generation numbers are dynamic; creating or terminating snapshots may cause generation numbers of other snapshots to change. This could be problematic in situations where multiple users create snapshots on the same set of volumes, especially in situations where a single volume is in multiple groups (Storage Groups, Device Groups, Composite Groups, and so on). As with any other feature or option, the user must make the best choice for their environment.