Log And Disk Group Planning; Log Size - HP 418800-B21 - StorageWorks Modular Smart Array 70 Storage Enclosure User Manual

Log contents
A small portion of log space is reserved for array commands. The largest portion stores host data that is
written to all of the virtual disks in the disk group.

Log and disk group planning

When you create a DR group pair, a log disk is automatically created for the source and destination DR
group. An important planning factor is selecting the disk groups in which to create the log disks.
Disk group category
• Select a disk group whose category is appropriate to the write mode of the DR group pair. See
write mode
determine the category the disk groups that are displayed in the replication manager.
Write mode
Enhanced asynchronous
Standard asynchronous
Synchronous
• If near-online disk groups cannot be made available, use the online disk groups that have the
most free space.
Disk group size
• When selecting a disk group, ensure there is space for log disks to expand to their maximum
size. See
• When creating disk groups, plan for the impacts of DR group logs.

Log size

When a DR group pair is created, the size of each log disk (source and destination) is 136 MB (Vraid1),
by default. The initial size is also called its minimum size.
When logging, the size automatically increases in proportion to the host data written to the DR group, up
to a preset maximum. By default, the maximum size is determined by the controller software. However,
you can manually set the maximum.
Log size example
maximum size
[varies]
^
^
^
initial (minimum) size
• The actual size and the requested size of a log are reported. When these differ, it indicates the
requested size change cannot be made until the log state changes.
• In synchronous write mode, the log is automatically returned to its minimum size when a merge
is completed or a full copy is performed. In enhanced asynchronous write mode, the log is not
returned to its minimum size when a merge is completed or when a full copy is performed.
• Sometimes a log can become much larger than is typically needed. In this case, HP recommends
that you edit the DR group properties and make the log smaller.
and online and near-online disk
Recommended disk group category
online
near-online
near-online
log size.
groups. You can use HP Command View EVA to
HP StorageWorks Replication Solutions Manager 4.0.1
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