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Dell EMC PowerMax and VMAX All Flash: TimeFinder SnapVX Local Replication
Executive summary Introduction TimeFinder SnapVX overview 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
GCM attribute
Open Replicator for Symmetrix (ORS)
TimeFinder SnapVX
TimeFinder Clone and VP Snap
TimeFinder/ Mirror
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

GCM attribute

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

GCM attribute

  • One of the architectural differences between PowerMaxOS 5978 and HYPERMAX OS 5977 compared to Enginuity 5876 is the doubling of track size, from 64K to 128K. An array running PowerMaxOS 5978 and HYPERMAX OS 5977 cannot create a device that is the same size as a device with an odd number of cylinders on an array running Enginuity 5876. To support full functionality, SRDF R1 and R2 pairs must be same size and TimeFinder source and target pairs must be the same size.

    HYPERMAX OS introduced a device attribute, geometry compatible mode (GCM). A device with GCM set is treated as half a cylinder smaller than its true configured size so the device will be treated as the same size as an Enginuity 5876 device with an odd number of cylinders, thus enabling full functionality between PowerMaxOS 5978 and HYPERMAX OS 5977 with Enginuity 5876 for SRDF, TimeFinder, and ORS.

    The GCM attribute can only be set for devices on arrays running PowerMaxOS 5978 and HYPERMAX OS 5977. The attribute can be set manually or automatically as part of an operation that creates a local or remote replication relationship.

    The symdev set /unset, symdg set/unset, symcg set/unset, and symsg set/unset commands have been enhanced with a new option -gcm to set and unset GCM for a device or group.

    The symdev show, symdev list –v, symdg show ld, symdg list ld –v, sympd show, and sympd list –v commands have been enhanced to report the GCM attribute.

    The symrdf createpair command has been enhanced to transparently set/unset the GCM attribute as part of the create pair operation, as follows:

    Set the GCM attribute for a target device that is configured half cylinder larger. The source of the copy can be:

    A device on an array running Enginuity 5876 with an odd number of cylinders and capacity that matches the GCM size of the device.

    A GCM device on an array running PowerMaxOS 5978 or HYPERMAX OS 5977.

    Unset the GCM attribute for a target device that is configured the exact same size as the source of the copy. The source of the copy can be:

    A device on an array running Enginuity 5876 with even number of the cylinders and capacity that matches the size of the device on the array running PowerMaxOS 5978 or HYPERMAX OS 5977.

    A device on the array running PowerMaxOS 5978 or HYPERMAX OS 5977 without the GCM attribute.