Logging; Log Merging - HP 418800-B21 - StorageWorks Modular Smart Array 70 Storage Enclosure User Manual

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
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
• 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
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
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
• 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
106 DR Groups
replication.
mode. This returns the log to its minimum size.
write mode.
log size.
virtual disk guidelines.
full copy mode.