Pool specifications and requirements

To calculate the pool capacity, use the following formulas.

• pool-capacity (MB) = total-number-of-pages * 42 - 4200.

  42 in the formula is size (MB) for one page and 4200 in the formula is the size (MB) of the management area on the pool-VOL with system area.

• To calculate the total number of pages, add up the number of pages obtained by using the following formula:

  number-of-pages = floor(floor(number-of-blocks-on-pool-VOL / 512) / 168)

  floor( ): Truncates the value calculated from the formula in parentheses after the decimal point (that is, round down to nearest whole number).

The minimum capacity of one pool is 3990 MB.

The following are the maximum capacities of one pool:

• A pool containing external volumes: 4.0 PB
• A pool containing internal volumes: 2.99 PB

The maximum total capacity of all pools in a storage system is 16.6 PB.

If you operate a pool without monitoring the free space, then ensure that the total V-VOL capacity remains smaller than the pool capacity.

You can reclaim zero pages and release the appropriate pages if the status of all data in the pages in the V-VOL reads no logical records (referred to as zero page). The free capacity of a pool increases after the pages are released.

The number of pool-VOLs in the entire pool can be calculated by adding up the values.

8 GB to 4.0 TB (8 GB to 256 TB for external volumes with the data direct mapping attribute)

The largest number of pools is 128. Assign a pool number in the range 0~127 as the identifier.

You can set the subscription limit to Unlimited by leaving this field blank. Set the subscription limit to Unlimited when you create the pool that contains DRS-VOLs.

• Warning threshold: You can set the value between 1% and 100%, in 1% increments. The default is 70%.
• Depletion threshold: You can set the value between the warning threshold and 100%, in 1% increments. The default is 80%.

If the pool-used capacity is equal to or greater than the warning threshold or the depletion threshold, a service information message (SIM) is issued by the storage system.

Thresholds cannot be defined for a pool with data direct mapping enabled.

If the pool-VOLs contain SSD parity groups, configure the pool so that the configurations of the SSD parity groups in the pool are the same between CBX pairs. See Configuration 1 in the figure below: Recommended and non-recommended configurations to get optimal performance in pools containing SSD parity groups.

Specifically, make sure that the following items match:

• Drive type
• Drive capacity
• RAID level of the parity group (including the drive configurations such as 14D+2P
• The number of parity groups

Note: Do not configure the following pools:

• The number of SSD parity groups in the pool is not the same between CBX pairs. See Configuration 2 in the figure below: Recommended and non-recommended configurations to get optimal performance in pools containing SSD parity groups.

  If one pool is configured without allocating parity groups evenly between CBX pairs, low throughput and response delays might occur due to a parity group bottleneck in the CBX pair with the fewest number of parity groups.

• A pool contains DP-VOLs in a CBX pair with no parity groups.

  See Configuration 3 in the figure below: Recommended and non-recommended configurations to get optimal performance in pools containing SSD parity groups.

  I/O operations to the DP-VOL in the additional CBX pair cause data transfer to the CBX pair with parity groups, which result in permanently increasing the total load on the storage system.