Concept Guide

Figure 11. MDSM Snapshot Volume View

How SRA uses snapshots

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.

-->

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