Equivalent Copy (EC)
The Equivalent Copy feature of AdvancedCopy Manager invokes a process of synchronization between source and destination volumes to create a synchronized copy of the source volume. The purpose of the synchronization is to reach and maintain a state of equivalence with the source volume in order to create a temporary copy or archival backup.
The source volume remains available and accessible as there is no need to stop or suspend access to the source volume while the copy is built using the synchronization process.
When a state of equivalence with the source volume has been attained, the destination volume continues to be maintained as an image of the source volume.
At any subsequent point while the source volume and the destination copy are in this state of equivalence, the destination copy can be split from the source, thus creating a backup with history or a replica copy as at that point in time.
Equivalent Copy is highly effective for:
Making backups much more quickly than with conventional backup processes, because backup data can be collected in parallel with ordinary transactions
Reducing processing time and costs by means of distributed processing using copy data
Figure 2.5 Equivalent Copy (EC)
Suspend/Resume Function (EC)
The Suspend/Resume option of the AdvancedCopy Manager Equivalent Copy (EC) function is used to create a backup after an initial copy has been built using the EC synchronization process. At this point, the copy source and copy destination volumes (Volume Pair) will have attained a state of equivalence.
The EC session is then suspended using the Suspend option, detaching the destination volume from the EC session to create a copy which can be used as a backup with history or as a source volume for a subsequent copy to an archive device. This copy could also be mounted and become available for use by other applications.
While the session is suspended all updates to the copy source volume continue to be tracked so that they can be applied to the destination volume should that EC session be subsequently resumed.
This allows the same destination volume to be reused as the base for a continuing backup, thus reducing the time required for backup.
The Resume option will invoke a re-synchronization process of the same source and destination volume pair where all of the tracked changes to the source volume will be applied to the destination volume to attain a state of equivalence again.
A suspend and resume process can be performed on the same volume pair as many times as required.
Figure 2.6 Suspend/Resume function (EC)
Remote Equivalent Copy (REC)
Remote Equivalency Copy (REC) is used to perform EC in the following circumstances:
REC replication is possible between different ETERNUS disk storage systems but hosted by a common Storage Server. These may exist on the same SAN but may be in geographically remote locations.
REC Replication is possible between ETERNUS disk storage systems hosted by different Storage Servers.
REC has two transmission modes; synchronous and asynchronous.
Synchronous mode guarantees that the copy destination will always match the copy source.
Asynchronous transfer mode is typically used in the following circumstances:
where there may be a significant communications lag between the devices
used to avoid adversely affecting server performance and write performance on the copy source.
Asynchronous mode has two primary sub-modes which provide greater control over data transmission according to transaction intensity and or data volume, or available bandwidth between copy source and copy destination.
The default Asynchronous mode must however be selected to perform a split (create a backup or replica).
REC is highly effective for:
Remote backup of a disaster countermeasure system or similar
Figure 2.7 Remote Equivalent Copy (REC)
