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Allocating Space for Protection Groups

Updated: October 22, 2010

Applies To: System Center Data Protection Manager 2010

When you create a protection group and select disk-based protection, you must allocate space on the storage pool for the replicas and recovery points for each data source that you have selected for membership in the group, and you must allocate space on protected file servers or workstations for the change journal.

DPM provides default space allocations for the members of the protection group. The following table shows how DPM calculates the default allocations.

How DPM Calculates Default Space Allocations

 

Component Default Allocation Location

Replica volume

For files:

  • (Data source size x 3) / 2

For Exchange data:

  • Data source size x (1 + log change) / (alert threshold - .05)

For SQL Server data:

  • Data source size x (1 + log change) / (alert threshold - .05)

For Windows SharePoint Services data:

  • Total size of all databases/ (alert threshold - .05)

For Virtual Server data:

  • Data source size x 1.5

For system state:

  • (Data source size x 3) / 2

For Hyper-V

  • Data source size x 1.5

DPM storage pool or custom volume

Recovery point volume

For files:

  • (Data source size x retention range in days x 2) / 100 + 1600 MB

For Exchange data:

  • 4.0 x retention range in days x log change x data source size + 1600 MB

For SQL Server data:

  • 2.5 x retention range in days x log change x data source size + 1600 MB

For Windows SharePoint Services data:

  • 1.5 x retention range in days x log change x total size of all databases + 1600 MB

For Virtual Server data:

  • (Data source size x retention range in days x 0.02) + 1600 MB

For system state:

  • (Data source size x retention range in days x 2) / 100 + 1600 MB

For Hyper-V

  • (Data source size * recovery range in days * 0.1) + 1600 MB

DPM storage pool or custom volume

Change journal (for file protection only)

300 MB

Protected volume on the file server or workstation

The values used in the preceding table are defined as follows:

  • Alert%—Threshold for the alert associated with replica growth; typically 90%.

  • Log change—This is the change rate on the database or storage group in question. This varies widely, but for the purposes of the default recommendation in DPM, it is assumed to be 6% for Exchange and SQL Server data and 10% for Windows SharePoint Services data.

  • Retention range (RR)—This is the number of recovery points stored; it is assumed to be 5 for purposes of the DPM default recommendation.

  • System state data source size—The data source size is assumed to be 1 GB.

When you create a protection group, in the Modify Disk Allocation dialog box, the Data Size column for each data source displays a Calculate link. For the initial disk allocation, DPM applies the default formulas to the size of the volume on which the data source is located. To apply the formula to the actual size of the selected data source, click the Calculate link. DPM will determine the size of the data source and recalculate the disk allocation for the recovery point and replica volumes for that data source. This operation can take several minutes to perform.

We recommend that you accept the default space allocations unless you are certain that they do not meet your needs. Overriding the default allocations can result in allocation of too little or too much space.

Allocation of too little space for the recovery points can prevent DPM from storing enough recovery points to meet your retention range objectives. Allocation of too much space wastes disk capacity.

If, after you have created a protection group, you discover that you have allocated too little space for a data source in the protection group, you can increase the allocations for the replica and recovery point volumes for each data source.

If you discover that you have allocated too much space for the protection group, the only way to decrease allocations for a data source is to remove the data source from the protection group, delete the replica, and then add the data source back to the protection group with smaller allocations.

To help you estimate your storage space needs, download the DPM storage calculator.

See Also

 
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