Learn About Estimating FlashCopy Repository Logical Drive Life Expectancy

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During the creation of a FlashCopy logical drive you are asked to define various properties for the FlashCopy repository logical drive , including the FlashCopy repository logical drive's name, capacity, a logical drive-to-LUN mapping, and the repository full condition. When defining the FlashCopy repository logical drive's properties, you should keep in mind what kind of usage you have planned for the FlashCopy logical drive. Understanding how the FlashCopy logical drive will be used can help you to estimate the life expectancy of the FlashCopy repository logical drive.

If numerous I/O requests are written to the base logical drive, the FlashCopy repository logical drive, which contains the FlashCopy data (information about the FlashCopy) and copy-on-write data, could eventually exceed the base logical drive capacity if all the original data blocks are changed. The default setting suggests 20% of the base logical drive 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 FlashCopy repository logical drive. It should be noted that this should be used merely as a guide, and that a FlashCopy repository logical drives life expectancy should be carefully re-estimated periodically.

Procedure

1

Highlight the FlashCopy repository logical drive in the Logical View. Select Logical Drive >> Properties and choose the Capacity tab or right-click on the FlashCopy repository logical drive and select Properties, then the Capacity tab.

2

Highlight the FlashCopy repository logical drive in the Logical View. Select View >> Go To >> FlashCopy Logical Drive or right-click on the FlashCopy repository logical drive and select Go To FlashCopy Logical Drive.

3

Record the creation timestamp 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 FlashCopy repository logical drive.

Based on the results, you should now be able to make an informed decision on whether you should increase the capacity of the FlashCopy repository logical drive. If the repository capacity will become 100% full during the FlashCopy's expected lifetime, then you should increase the FlashCopy repository logical drive's capacity. For more information, see Increasing the Capacity of a FlashCopy Repository Logical Drive.

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