Dell PowerVault MD Series Storage Arrays Storage Replication Adapter (SRA) Best Practices Guide (Client)

The MD Series SRA utilizes Point-in-Time Snapshots if the feature is enabled on the storage array during test failover, the SRA creates a Snapshot Group, Snapshot Image, and Snapshot Volume on the recovery site’s storage array for all volumes contained in the protection groups being tested. This requires the creation of the two snapshot repositories listed above and the default size for these repositories is 10 percent of the base volumes for each repository, for a total of 20 percent of the base volume size. This means that the amount of free capacity on the recovery site storage array must be 20 percent of the base volumes participating in the test failover. This value is controlled by the SraConfigurationData.xml file located in the config directory under the installation directory, typically:

C:\Program Files (x86)\VMware\VMware vCenter Site Recovery Manager\scripts\SAN\Dell\SraConfigurationData.xml

The value is set with the XML tag <SnapshotBasePercentage>.

<!--
                                 SnapshotBasePercentage represents the initial size, expressed as a percentage of volume size, of a snapshot which is formed
                                 for test failover.
                                 -->
                                 <SnapshotBasePercentage>10</SnapshotBasePercentage>
                              

Based on how the VMs are used during test failover, it is possible to fine-tune this value for your environment to reduce the amount of free capacity needed for test failover. If the test VM residing on the recovery site ESX host does not write extensive data to the Datastores and no synchronization (or minimal changes) occur between the protected site volumes and the recovery site volumes during test failover, this value may be decrease to 2–5 to require even less free capacity during test failover. The Snapshot Volume and Snapshot Group repositories are deleted during the cleanup phase of test failover along with the Snapshot Image.

Because the Snapshot Volume is typically not used during the test failover process (little write activity), the size of these repositories may be decreased to small sizes in order to preserve free capacity on the recovery site’s storage array. If a repository runs out of space during the test failover phase, the VMs on the recovery site lose access to the Datastore and underlying volume affected by the out-of-space condition of the repository, but the protected site VM functions as normal. These values are not recommended for Snapshot repositories used for other purposes. To monitor the sizes and status of the repositories, in the left pane, click All Logical Objects. In the working pane, from the Object Type drop-down menu, select Repositories.

To view the repository space, mode, or timestamps, from the drop-down menu, select Volumes or Snapshot Groups.