Understanding Protection for CSV
Updated: April 21, 2010
Applies To: System Center Data Protection Manager 2010
A common Cluster Shared Volume (CSV) deployment has the virtual hard disks (VHDs) of the virtual machines on a CSV, with virtual machines distributed across the nodes of the cluster. Each virtual machine has direct I/O access to its respective VHD on the CSV.
In this example, when VM2 is being backed up, the CSV is made local to Node B. All I/O for VM1 is then routed over the network through the CSV filter on Node B. This affects the performance of VM1 and it appears on the Failover Cluster Manager as being in “redirected I/O mode.”
To reduce the impact on VM1, we recommend that you use hardware snapshots, which enable the CSV to resume direct I/O mode as soon as the hardware snapshot has been created. The duration of this process is typically very short, about two minutes.
If you use software snapshots, the CSV will be in redirected I/O mode for all virtual machines on this CSV, other than VM2, for the duration of the backup. The duration of this process depends on the size of the VHDs being backed up by DPM, and can be significant. Therefore, using software snapshots can decrease the performance of the virtual machines.
After the snapshot is created, DPM starts replicating the data from the snapshot to the DPM server. After the replication is complete, the protection agent deletes the hardware snapshot.