HP 418800-B21 HP StorageWorks Replication Solutions Manager 4.0.1 user guide ( - Page 111

IMPORTANT: You cannot remove virtual disks from a DR group pair when remote replication is suspended. Write mode (async/sync replication) The replication write mode of each DR group pair can be asynchronous or synchronous. The choice is generally a business decision based on your goals and the bandwidth of the intersite link. For details, see the HP Continuous Access EVA Performance Estimator user guide. Unless specified otherwise, replication write mode is set to synchronous when you create a DR group pair. Write mode comparison (summary) Best data protection Synchronous Best host I/O performance Asynchronous Asynchronous write mode In asynchronous write mode, the source array acknowledges host writes before the data is replicated on the destination array. This process allows faster host I/O than with synchronous. From a data protection standpoint, there can be brief instances in which the data is not identical on the source and destination DR group. Asynchronous write mode can be standard or enhanced, depending on the controller software version. See controller software version - remote replication features. The following is a summary of standard and enhanced operation. Standard asynchronous operation Enhanced asynchronous operation 1. Host data written to the virtual disks in a source DR group is stored in a write-pending cache on the source array. 2. The source array acknowledges the writes to the host. 3. The source array replicates the data in the write-pending cache to the destination array. 4. The destination array writes the data to the virtual disks in the destination DR group and acknowledges completion back to the source array. 1. Host data written to the virtual disks in a source DR group is stored in a write-pending cache on the source array. 2. The source array copies the cached data to the source DR group log. 3. The source array acknowledges the writes to the host. 4. The source array replicates the data in the DR group log to the destination array. 5. The destination array writes the data to the virtual disks in the destination DR group and acknowledges completion back to the source array. IMPORTANT: If a source and destination array are not running the same implementation of write mode (standard or enhanced), then only synchronous write can be selected. Synchronous write mode In synchronous write mode, the array acknowledges I/O completion after the data is cached on the source and destination arrays. This process maintains identical data on a source DR group and its destination DR group at all times. The following is a summary of synchronous operation. HP StorageWorks Replication Solutions Manager 4.0.1 111