How does disk allocation work?

Published : April 8, 2005 | Updated : August 17, 2005

When you create a new protection group, Data Protection Manager (DPM) allocates disk space for the protection group in the storage pool. Based on the size of the protected volume, DPM recommends the amount of disk space to allocate in the storage pool, and verifies that the file server contains sufficient space for the synchronization log.

If you are only protecting a subset of the data on the protected volume, you can calculate the size of the protected data so that DPM can adjust its recommendations for disk allocation. If the data on the protected volume outgrows the initial allocations, DPM generates a “Disk threshold exceeded” alert and provides guidance for increasing disk allocations appropriately. During creation of a protection group, DPM allocates disk space according to the guidelines shown in the following table:

Protection Element

Minimum Disk Space

Location

Replica

The larger of:

  • 1.5 times the size of the used space on the protected volume, or the total size of the protected volume, whichever is smaller

  • 1.5 GB

DPM storage pool

Shadow copies

The larger of:

  • 20% of the space allocated for the replica

  • 550 MB

DPM storage pool

Synchronization logs

The larger of:

  • 10% of the size of the protected volume

  • 500 MB

Protected volume on the file server

Transfer logs

The larger of:

  • 1.4 times the size of the synchronization log

  • 700 MB

DPM storage pool

You should accept the recommended disk allocations for the protection group unless you are sure that these allocations will not meet your requirements. If you change the recommended allocations, you may get fewer shadow copies than you wanted or DPM may allocate more disk space than is needed. Generally, the recommended allocations provide sufficient storage for at least a couple of weeks of shadow copies. If necessary, you can adjust the disk allocations after monitoring disk usage for data protection.

You can schedule and view reports in the Reporting task area. To view trends in disk usage for a protection group, review a Disk Utilization report.

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