HP 418800-B21 HP StorageWorks Replication Solutions Manager 4.0.1 user guide ( - Page 106
Logging, Log merging
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Default maximum size The default maximum size depends on the controller software version and equals the DR group size multiplied by a factor. For example, if a DR group contains virtual disks with a total of 10 GB and the factor is 1x then the default maximum size is 10 GB. For specific factors, see controller software features - remote replication. Log size and disk group occupancy warnings The size of a log disk can cause a disk group occupancy warning. See disk group occupancy alarm level. If this happens, consider the following options: • Temporarily stop host I/O to the virtual disks in the impacted DR group and plan necessary changes. • Allow the log to completely fill and trigger an automatic full copy, or manually force a full copy. See full copy mode. This returns the log to its minimum size. • Add storage to the disk group that the log disk is in. • Delete unneeded virtual disks or containers in the disk group to create more free space. Logging The process of storing host write-transactions to the virtual disks in a source DR group, in the exact order received, is called logging. The details of the logging process depend on remote replication write mode. See write mode. Logging when in enhanced asynchronous write mode When using enhanced asynchronous write mode, logging occurs continuously, even if replication is not suspended or the destination is available. In effect, the log continuously acts as a first-in-first-out (FIFO) buffer, accepting host write-transactions in and replicating them out to the destination. In many cases, an asynchronous log can buffer up to several days of host write-transactions, depending on the log size and the transaction rate. Logging when in synchronous write mode When in synchronous write mode, logging occurs only if replication is suspended or the destination is not available. When replication is resumed or the destination becomes accessible the logged host write-transactions are merged to the destination. See merging. Log-full event When log is full and its size cannot be increased, a full copy is automatically started. See full copy mode. The controller software considers a log to be full when any of the following occur: • The log disk reaches its maximum log size. • The log disk reaches the maximum size for a disk. See virtual disk guidelines. • No free space remains in the disk group that contains the log disk. Log merging The process of replicating a log's host write-transactions to a destination DR group, in the same order as received, is called merging. • In asynchronous write mode, merging occurs whenever required and the destination is available. • In synchronous write mode, merging occurs when replication is resumed and the destination is available. When a merge is complete, the log disk is automatically returned to its minimum size. See log size. 106 DR Groups