Estimating the Life Expectancy of a Snapshot Repository Virtual Disk

When you create a snapshot virtual disk, you must define these properties for the snapshot repository virtual disk:

When you define the snapshot respository virtual disk properties, you must know how you plan to use the snapshot virtual disk. If you know how you plan to use the snapshot virtual disk, you can estimate the life expectancy of the snapshot repository virtual disk. The snapshot repository virtual disk contains the snapshot data and the copy-on-write data. The snapshot data is information about the snapshot.

For example, if many I/O requests are written to the source virtual disk, the snapshot repository virtual disk could exceed the source virtual disk capacity if all of the original data blocks are changed. The default setting is 20% of the source virtual disk capacity. This value can be adjusted over time.

Use this guide to estimate the life expectancy for a snapshot respository virtual disk. Use this guide and periodically update the estimate.

  1. Record the creation date and the creation time for the snapshot repository virtual disk.
  2. Record the capacity used (GB) and the available capacity (GB).
  3. Determine the elapsed time (t) by subtracting the creation time from the current time. Express the elapsed time in either minutes, hours, or days.
  4. Use this equation to calculate the total time (Tr) that the snapshot repository virtual disk is available for copy-on-write data.

Tr = (t * Ct)/Cu

Tr = Total time available

t = Elapsed time

Ct = Available capacity

Cu = Used capacity

Based on the results, you can decide how much to increase the capacity of the snapshot repository virtual disk. If the snapshot repository virtual disk will become 100% full during the expected life time, you should increase the capacity of the snapshot repository virtual disk.

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