Global-active device (GAD) enables you to create and maintain synchronous, remote copies of data volumes. A virtual storage machine is configured in the primary and secondary storage systems using the actual information of the primary storage system, and the global-active device primary and secondary volumes are assigned the same virtual LDEV number in the virtual storage machine. This enables the host to see the pair volumes as a single volume on a single storage system, and both volumes receive the same data from the host. A quorum disk, which can be located in a third and external storage system or in an iSCSI-attached host server, is accessed by both storage systems and is used to monitor the pair volumes for any communication failure.
Ops Center Automator includes a Global-Active Device Setup service template that enables you to automation a portion of the GAD setup process. In addition, a number of other service templates support global-active device (GAD) configurations. GAD enables read/write copies of the same data in two places at the same time for continuous mirroring. Ops Center Automator supports three GAD configurations:
- Single-server configuration
- Server-cluster configuration
- Cross-path configuration
Cross-path suppression
If the distance between the primary site and the secondary site is long, I/O using the cross-path causes overhead. Suppress I/O of the cross-path by setting ALUA (Asymmetric Logical Unit Access) or HMO (Host Mode Option).
Additional cross-path suppression problems
- If the Alternate path software supports ALUA (Asymmetric Logical Unit Access), suppress the cross-path by setting ALUA to the preferred path.
- If the Alternate path software does not support ALUA, you cannot suppress cross-path.
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If you are using Dynamic Link Manager (HDLM), suppress the cross-path by setting a nonpreferred path to the HMO.