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Calculating Capacity Requirements

Updated: November 1, 2008

Applies To: System Center Data Protection Manager 2007

Capacity requirements for the DPM storage pool are variable and depend primarily on the size of the protected data, the daily recovery point size, expected volume data growth rate, and retention range objectives.

Daily recovery point size refers to the total size of changes made to protected data during a single day. It is roughly equivalent to the size of an incremental backup. Retention range refers to the number of days for which you want to store recovery points of protected data on disk. For files, DPM can store a maximum of 64 recovery points for each volume included in a protection group, and it can create a maximum of 8 scheduled recovery points for each protection group each day.

noteNote
The limit of 64 recovery points for files is a result of the limitations of the Volume Shadow Copy Service (VSS), which is necessary for the end-user recovery functionality of DPM. The recovery point limit does not apply to application data.

In general, we recommend making the storage pool two times the size of the protected data for protection of files. This recommendation is based on an assumed daily recovery point size of approximately 10 percent of the protected data size and a retention range of 10 days (two weeks, excluding weekends).

If your daily recovery point size is larger or smaller than 10 percent of your protected data size, or if your retention range objectives are longer or shorter than 10 days, you can adjust the capacity requirements for your storage pool accordingly.

Regardless of how much capacity you decide to allow for the storage pool in your initial deployment, we recommend that you use extensible hardware so that you have the option of adding capacity should the need arise.

The sections that follow provide guidelines for determining your daily recovery point size and retention range objectives.

Estimating Daily Recovery Point Size

Our recommendation to make the storage pool two times the size of the protected data assumes a daily recovery point size of 10 percent of the protected data size. Daily recovery point size is related to data change rate and refers to the total size of all recovery points created during a single day. To get an estimate of the daily recovery point size for your protected data, you can review an incremental backup for a recent, average day. The size of the incremental backup is usually indicative of the daily recovery point size. For example, if the incremental backup for 100 GB of data includes 10 GB of data, your daily recovery point size will probably be approximately 10 GB.

Determining Retention Range Objectives

Our recommendation to make the storage pool two times the size of the protected data assumes a retention range objective of 10 days (two weeks, excluding weekends). For the typical enterprise, requests for recovery of data are concentrated within two to four weeks after data loss events. A retention range of 10 days provides for recovery of data up to two weeks after a data loss event.

The longer your retention range objective, the fewer recovery points you can create each day. For example, if your retention range objective is 64 days, you can create just one recovery point each day. If your retention range objective is eight days, you can create eight recovery points each day. With a retention range objective of 10 days, you can create approximately six recovery points each day.

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