During the creation of a
The default setting for the snapshot repository virtual disk capacity is 20% of the source virtual disk's capacity and, in general, this capacity should be sufficient. However, use the following information to help determine the appropriate capacity of the snapshot repository virtual disk:
Important: Using a
utility to perform a defragment operation on a with an associated snapshot repository virtual disk will cause a copy-on-write of every data block in the source virtual disk. This can cause the snapshot repository virtual disk to fill before the defragment operation is completed and the snapshot virtual disk will fail or writes will fail to the source virtual disk, depending on the snapshot virtual disk full condition that was originally set for the snapshot virtual disk. To prevent any failures during a source virtual disk defragment operation, ensure that the snapshot repository virtual disks' capacity is set to 105% of the size of the source virtual disk before starting the defragment utility. This is the minimum size needed to support a copy-on-write of every data block in the source virtual disk.
Use the following formula to calculate the amount of management overhead required to store snapshot data on the snapshot repository virtual disk. This formula should be used merely as a guide, and snapshot repository virtual disk capacity should be re-estimated periodically.
Note: Conversion from bytes, to kilobytes, and then to megabytes is required for this formula.
The formula to calculate the amount of management overhead required is:
192 KB + (X/2000)
where X is the capacity of the source virtual disk in bytes.
Example:
For a 5 GB source virtual disk, where 30% of the data blocks are expected to change on the source virtual disk, the estimated snapshot repository virtual disk capacity can be calculated as follows:
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1 |
Convert the source virtual disk's capacity to bytes. When converted, 5 GB equals 5,368,709,120 bytes. |
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2 |
Divide the source virtual disk's capacity (in bytes) by 2000. When divided, the result is 2,684,354.56 bytes |
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3 |
Convert the result from step 2 (in bytes) to kilobytes (KB). When converted, the result is 2621.44 KB. |
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4 |
Add 192 KB to the results from step 3. 192 KB + 2621.44 KB = 2813.44 KB |
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5 |
Convert the result from step 4 to megabytes (MB). When converted, the amount of management overhead required is calculated to be 2.75 MB (or 0.002686 GB). |
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6 |
In this example, 30% of the data blocks on the source virtual disk are expected to change. To accurately calculate the snapshot repository virtual disk capacity, sufficient space would need to be allowed for the copy-on-write data as well as the management overhead (calculated in step 5). To calculate the copy-on-write space required, calculate the percentage of the source virtual disk expected change: 30% of 5 GB = 1.5 GB The final estimated snapshot repository virtual disk capacity for this example is: 1.5 GB + 0.002686 GB = 1.502686 GB |
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7 |
In the Create Snapshot Virtual Disk Wizard: Specify Repository Capacity dialog, use the percentage (%) of source virtual disk spinner box to set the estimated snapshot repository virtual disk capacity. Note: The spinner box sets the snapshot repository virtual disk capacity as a percentage of the source virtual disk. Using the spinner box, increase or decrease the percentage until the Snapshot Repository Virtual Disk Capacity value matches the estimated capacity calculated in step 6. (Some rounding up might be required.) |
Learn About Estimating Snapshot Repository Virtual Disk Life Expectancy
Increasing the Capacity of a Snapshot Repository Virtual Disk