HP 418800-B21 HP StorageWorks Replication Solutions Manager 4.0.1 user guide ( - Page 109

• The destination DR group was unavailable after power was cycled off and on in the source array. • Remote replication was not suspended after power was cycled off and on in the source array. • The Destination mode was other than Read Only after power was cycled off and on in the source array. You can determine if disk presentation is blocked by checking the operational state of the DR group or individual disk. See viewing DR group properties and viewing virtual disk properties. Unblocking The virtual disks in a source DR group are automatically unblocked when the destination DR group becomes available again. You can manually unblock virtual disks by suspending the source DR group in which they are members. See suspending a DR group pair. Presentation blocking provides protection Disk presentation blocking is a feature that is similar to failsafe operation. See failsafe mode. Blocking can provide the following: • Data consistency during a site failure, when a source and its destination virtual disk could be simultaneously presented to different hosts. • Protection in stretched-host clusters, against host members accessing two copies of the same data. • Protection for boot-from-SAN servers, against two hosts booting from the same boot image. Remote replication guidelines Storage arrays • Source and destination arrays must have remote replication licenses. See replication licenses overview. • The array selected for the destination DR group depends on the remote replication configuration. For supported configurations, see the HP StorageWorks Continuous Access EVA planning guide. • A storage array can have DR group relationships with up to two other storage arrays. • The maximum number of virtual disks in a DR group and the maximum number of DR groups per array vary with controller software versions. See controller software features - remote replication. DR groups and failover • Failover of a DR group pair is permitted only by specifying a destination DR group. • When failsafe mode is enabled, a DR group pair cannot be suspended. See failsafe on unavailable member, suspend on failover. • When a DR group pair is suspended, it cannot be failed over or reverted to home. • A DR group cannot be deleted if a virtual disk in the destination DR group is presented. • For additional help on usage, see using DR groups. Log disks • Logs disks for the source and destination DR groups should be kept the same size. • The log size cannot be changed when in enhanced asynchronous write mode. See write mode. Write mode • The write mode cannot be changed if the source log disk is in use or contains data. Before changing, a non-empty source log disk must be merged to its destination. • If a source and destination array are not running the same implementation of write mode (standard or enhanced), then only synchronous can be selected. HP StorageWorks Replication Solutions Manager 4.0.1 109