Disk Space Usage and Retention

An everRun system that takes snapshots and has DR protection enabled requires a larger volume container. The size of the volume container depends largely on the amount of data that is written to the volume between snapshots. This amount varies for different applications and different RPO values.

For a typical case with 10 or fewer DR-retained snapshots and with an additional 3 user-created snapshots:

• For a VM created with a separate boot disk, or for applications that write relatively small amounts of data between snapshots, a reasonable volume-container size is 2.6 times larger than the volume size.
• For applications that write moderate amounts of data between snapshots, a reasonable volume-container size is approximately 3.5 times larger than the volume size.
• For applications that write larger amounts of data between snapshots, the volume-container size may be more than 3.5 times larger than the volume size.

 A general formula for calculating the approximate volume-container size is:

Before you use the preceding formula, you must calculate SnapshotSize:

1. During peak business hours, take four or more snapshots of the primary VM in sequence with a time of (TargetRPO) / 2 between them. For example, if the RPO is set for 2 hours, the software takes a snapshot every hour.
2. Then, for each of the VM's volumes, look into its volume container.
   1. Ignore the first volume snapshot.
   2. For the remaining volume snapshots, calculate the average of the three largest volume snapshots. This average is SnapshotSize.

Related Topics

Disaster Recovery Terminology