HP XP RAID Manager Software - Manual (Page 14)

longer a snapshot is held, and the more snapshots that exist all result in more data accumulating
in the data pool.
For more information about data pool sizing, see “Sizing the data pool workflow” (page 14) .
Sizing the data pool workflow
Updating the P-VOL replaces and holds the P-VOL data in the data pool. The original data in the
data pool is held to maintain the image of the P-VOL at the time of the snapshot.
To determine the size of the data pool, do the following:
1. Measure write workload over time from the host software application to the P-VOL. Write
workload is the megabytes-per-second that are written to the P-VOL over a specific amount of
time.
2. Calculate the amount of data that would accumulate during the lifespan of your V-VOLs.
3. Multiply the amount of data that accumulates by the number of V-VOLs.
The following figure shows the basic factors for data pool sizing.
When you finalize the capacity for a data pool, factor in the following:
•
A safety factor of 20 percent. Having a safety factor calculated in minimizes the chances of
over-filling the data pool. To factor in a safety factor of 20 percent, multiply the base data
pool size by 1.2.
•
Annual increase in data transactions. Your business data is likely to grow. Multiply the base
pool size by the percentage of expected annual growth.
•
The unit size of 256 KB. Data is copied to a pool in units of 256 KB. This is true even when
the actual write data is smaller than 256 KB. In such a case, the write consumes 256 KB of
the pool-VOL capacity.
Calculating the number of Snapshot pairs
The available system resources for copying pairs limits the number of SS pairs that you can create
in the storage system. Confirm with your service provider that additional shared memory for
differential tables and the V-VOL management area are installed on your system.
14 Business Copy/Snapshot planning and design