HP StorageWorks Continuous Access EVA Administrator Guide (T3687-96043, December 2005)

5 Managing remote replication

This chapter describes replication routine and advanced procedures.

Using remote replication in a mixed EVA environment

Speciﬁc remote replication features depend on the controller software version. The following rules

apply to remote replication between an array with XCS controller software and an array with VCS

controller software:

• If a feature i

s supported differently in the source and destination arrays, such as the supported

number of virtual disks in a D R group, the more restrictive value applies to the source-destination

pair.

• If a feature

is not available in both arrays, the feature cannot be used in a source-destination pair.

For version-speciﬁ c features and current support lim its, see the EVA replication software rele ase notes.

Managing merges and full copy

When logging occurs on a source array, there is a temporary disparity between data being processed at

the local site and the data that exists at the remote site. A merge or full copy corrects this disparity when

the reason for the interruption is remedied. A merge sends data from the log disk in write order so the

destination copy remains crash consistent. A full copy copies data in one–MB chunks from the source

virtual disk to the destination virtual disk, and data is inconsistent until the full copy is complete.

Throttling merge I/O after logging

Throttling is the channeling of merge I/O to merge critical data ﬁrst by suspending and resuming speciﬁc

DR groups.

When I/O h as been halted and links to the remote arrays are restored, DR groups not in failsafe-enabled

mode automatically resume replication. If there are dozens of DR groups with large logs, they compete

for bandwidth as they tr y to synchronize simultaneously. By suspending noncritical DR groups, the

controllers merge only the most critical data ﬁrst, allowing this data to be synchronized and become

accessible before the less important data. As the more important groups ﬁnish merging, resume the

I/O of the groups that were suspended.

Maintaining I/O performance while merging

During a merge, the controller software manages merge writes and host I/O, completing two merge

writes for every host I/O. This ratio ensures that the log empties faster than it ﬁlls. If host performance is an

issue during merging, you can postpone merging to a period of low demand. Use the suspend command

in the replication manager to prevent merging and then the resume com m a nd to allow m erging.

Prep

aring for a full copy

NOTE:

ABusinessCopyEVAlicenseisrequiredforthisprocedure.

When a D R group log is marked for a full copy, there is a risk to the destination copy once the process

begins. Creating a snapclone of the destination virtual disk b efore a full copy starts can eliminate this

HP StorageWorks Continuous Access EVA administrator guide