HP StorageWorks MSA2012i HP StorageWorks 2000 Modular Smart Array Reference Gu - Page 106
How much modified write data will the snapshots have?, 000 Mbyte
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■ How much modified (write) data will the snapshots have? Of the snapshots that will be mounted as read-write and actually written to, factor in the average amount of data that will be modified. ■ Add 750 Mbyte of reserve space for internal use. ■ Add a recommended 25% safety margin to the snap pool in case actual capacity use exceeds the estimate. You can estimate snap-pool size as shown in following example. Assume you want to create a snap-pool for two 10-Gbyte master volumes, and will use these values: ■ Master volume size = 10,000 Mbyte ■ Average percent of change = 5% (0.05) ■ Number of snapshots retained = 4 ■ Number of modified snapshots = 4 ■ Average write data = 1,000 Mbyte ■ Snap-pool reserve space = 750 Mbyte ■ Safety margin = 25% The snap-pool size calculation is: MV1 space (10,000 x 0.05 x 4) + (4 x 1000): 6000.00 Mbyte + MV2 space (10,000 x 0.05 x 4) + (4 x 1000): 6000.00 Mbyte + Snap-pool reserve space : 750.00 Mbyte -------- = Master volume space required : 12750.00 Mbyte x Safety margin : 1.25 -------- = Total snap-pool space required : 15937.50 Mbyte Therefore, the snap pool should be approximately 16,000 Mbyte (16 Gbyte). Note - If you cannot estimate the size values, you can specify a reasonable initial size and use the Auto Expand policy to expand the snap pool when it reaches a capacity threshold. See "Setting Snap Pool Policies and Thresholds" on page 110. Note - For an explanation of sizes represented by various units, see "Size Representations in SMU" on page 27 for more information. 106 HP StorageWorks 2000 Family Modular Smart Array reference guide • August 2008