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Dell PowerStore: Snapshots and Thin Clones
Executive summary Introduction
PowerStore overview
Snapshots overview
Redirect-on-write technology
Terminology
Snapshot operations Snapshot access Snapshot aging Snapshot properties Snapshot rules Snapshot interoperability Thin clone overview Thin clone operations Conclusion Appendix: Technical support and resources

Redirect-on-write technology

Redirect-on-write technology

  • PowerStore uses redirect-on-write technology for all writes entering the system. When a resource writes to a location which is shared with another resource or by a snapshot, the data is redirected to a new location and the resource pointers are updated to reference the new location. The following figure provides an example of redirect-on-write technology.

    Figure 1.        Redirect-on-write example

    In this example, a storage resource contains four blocks of data: A, B, C, and D. A snapshot is taken of the storage resource to preserve this point-in-time, and points to blocks A, B, C, and D. When the host/client modifies blocks B, A, then D, the data is written to new locations on the system. The pointers for the storage resource are then updated to reflect the new locations for B’, A’, and D’. This example assumes that no data-reduction savings are achieved. For more information about data reduction within PowerStore, see the white paper Dell PowerStore: Data Efficiencies on the PowerStore Info Hub.