Global-active device (GAD) is a type of remote synchronous data replication on Hitachi storage systems. UCP Advisor enables you to create global-active device pairs in single server, server cluster, and cross-path system configurations.
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, is used to monitor the GAD pair volumes. The quorum disk acts as a heartbeat for the GAD pair, with both storage systems accessing the quorum disk to check on each other. A communication failure between systems results in a series of checks with the quorum disk to identify the problem for the system able to receive host updates.
Global-active device provides the following benefits:
- Continuous server I/O when a failure prevents access to a data volume
- Server failover and failback without storage impact
- Load balancing through migration of virtual storage machines without storage impact
For more information about global-active device on Hitachi storage systems, see Global-Active Device User Guide (MK-92RD8072).