Estimating Snapshot Repository Virtual Disk Life Expectancy

During the creation of a  you are asked to define various properties for the  including the snapshot repository virtual disk's name, capacity, a , and the repository full condition. When defining the snapshot repository virtual disk's properties, keep in mind what type of usage you have planned for the snapshot virtual disk. Understanding how the snapshot virtual disk will be used can help you to estimate the life expectancy of the snapshot repository virtual disk.

If numerous I/O requests are written to the , the snapshot repository virtual disk, which contains the snapshot data (information about the snapshot) and  data, could eventually exceed the source virtual disk capacity if all the original data blocks are changed. The default setting suggests 20% of the  capacity, but this is a setting that can be fine tuned after some usage data becomes available.

The following procedure describes how to estimate the life expectancy of a snapshot repository virtual disk. It should be noted that this procedure should be used as a guide and that a snapshot repository virtual disk's life expectancy should be carefully re-estimated periodically.

1

Highlight the snapshot repository virtual disk in the Logical View by either selecting Virtual Disk >> Properties and choosing the Capacity tab, or right-clicking the snapshot repository virtual disk, selecting Properties, and selecting the Capacity tab.

2

Highlight the snapshot repository virtual disk in the Logical View by selecting View >> Go To >> Snapshot Virtual Disk, or right-clicking the snapshot repository virtual disk and selecting Go To Snapshot Virtual Disk.

3

Record the creation time stamp day and time.

4

Record the capacity used (GB) and the available capacity (GB).

5

Determine the elapsed time (t) by subtracting the creation time from the current time, expressing the elapsed time in either minutes, hours, or days.

The total time (Tr) the repository is available for copy-on-write data can now be estimated (based on the current usage) by multiplying the elapsed time (t) by the available capacity (Ct), then dividing the resultant number by the capacity used (Cu).

where:

Tr = Total time available

t = Elapsed time

Ct = Available capacity

Cu = Used capacity

Therefore:

Tr = (t * Ct) / Cu

Note: The Total Time Available (Tr) indicates the total usage time for the snapshot repository virtual disk.

Based on the results, you should now be able to make an informed decision on whether you should increase the capacity of the snapshot repository virtual disk. If the repository capacity will become 100 percent full during the snapshot's expected lifetime, then you should increase the snapshot repository virtual disk's capacity. For more information, see Increasing the Capacity of a Snapshot Repository Virtual Disk.

Related Topics

Learn About Estimating Snapshot Repository Virtual Disk Size

Learn About Snapshot Virtual Disk Maintenance