Adaptec 5325301638 Administration Guide - Page 71

Estimating Snapshot Pool Requirements Estimating Snapshot Pool Requirements Snapshot data grows dynamically for as long as a snapshot is active and as long as there is enough space available in the snapshot pool to store them. When the snapshot pool approaches its capacity (at about 95 percent), the Snap Server deletes the oldest snapshot's data to create space for more recent snapshot data. The default configuration allocates 80 percent of RAID capacity to the volume and 20 percent to the snapshot pool. You can adjust the size of the pool up (assuming unallocated space exists) or down according to your needs. If you find that your snapshot strategy does not require all of the space allocated to the snapshot pool by default, consider decreasing snapshot pool capacity and re-allocating the capacity to the file system. To adjust the size of the snapshot pool, navigate to the Storage > Snapshots screen, and click the Adjust Snapshot Space link in the introductory text. The number of snapshots that a RAID can support is a function of these factors: (1) the space reserved for the snapshot data; (2) the duration of the snapshots you create; and (3) the amount and type of write activity to the volume(s) since the snapshot was created. The following table describes minimum and maximum allocation cases. Guidelines for Estimating Snapshot Pool Requirements Allocate about 10% of RAID if Allocate about 25% of RAID if • Activity is write-light • Activity is write-heavy • Write access patterns are concentrated in • Write access patterns are randomized a few places across the volume • A small number of Snapshots must be available at any point in time • A large number of Snapshots must be available at any point in time Adjusting Snapshot Pool Size The current size of the snapshot pool for each RAID (or RAID group) can be viewed by navigating to the Storage > Snapshots screen and clicking the adjust snapshot space link in the introductory text. On the screen that opens, you can adjust the pool up or down as necessary at any time. In addition, there are two other processes that may affect the size of the snapshot pool. • Creating a Volume - In the course of creating a new volume, a pull-down menu allows you to add a percentage of the capacity being allocated to the new volume to the snapshot pool. This feature defaults to 20%, the recommended amount of space to reserve for snapshots. If you do not plan to use snapshots with this volume, maximize volume capacity by reducing this percentage to zero; if you do plan to use snapshots, adjust this percentage in accordance with the guidelines discussed in previous section. Chapter 7 Snapshots 57