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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

Reserved capacity

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

Reserved capacity

  • Reserved Capacity is a percentage of the SRP that can only be consumed by new host writes. Existing and new snapshots are affected if the Free Capacity of the SRP falls below the set Reserved Capacity. The following commands view and change the values:

    • symcfg list –srp –v
    • symconfigure -sid <sid> -cmd "set srp <srp_name> resv_cap=<value>;" commit

    Valid values for Reserved Capacity percentage are from 1% to 80%, and NONE.

    For example, if the reserved capacity on an SRP is set to 10% and the SRP becomes 90% full of volume allocations, snapshot deltas, and SRDF Delta Set Extension allocations, only new host writes can consume the last free 10% of the SRP.

    When only Reserved Capacity is available in an SRP, a snapshot fails at the next attempt to create a new snapshot delta, and the snapshot needs to be terminated. VP Snap and Clone Nocopy sessions also fail at the next write that requires a source track to be copied to target.

    Copy to targets stops and cannot complete. This includes SnapVX linked targets, Clone copy mode sessions, and TimeFinder/Mirror BCVs. Copy resumes if free space is made available in the SRP, or if the Reserved Capacity value is lowered enough.

    The Reserved Capacity affects the TimeFinder copy process only. Host reads and writes to the targets are still possible.

    VAAI XCOPY and ODX copy operations also obey the Reserved Capacity of an SRP. In these cases, the operation can continue by falling back to host-level copy which appears as host writes to the array rather than copy operations.