Pool-VOL requirements

While pool-VOLs can coexist with other volumes in the same parity group, for best performance:

• Pool-VOLs for a pool should not share a parity group with other volumes.
• Pool-VOLs should not be located on concatenated parity groups.

Pool-VOLs cannot be used for any other purpose. For instance, you cannot specify the following volumes as pool-VOLs:

• Volumes used by ShadowImage for Mainframe, TrueCopy for Mainframe, or Universal Replicator for Mainframe
• Volumes already registered in Dynamic Provisioning for Mainframe pools
• Volumes whose LDEV status is not Normal, Correction Access (modifying access attributes), or Copying (copying volume data)
• Command devices

The following pool-VOLs cannot exist in the same pool:

• Internal volumes with external volumes whose cache mode is disabled.
• External volumes whose cache mode is enabled and external volumes whose cache mode is disabled.

• RAID 5 (3D+1P)
• RAID 6 (6D+2P, 14D+2P)

Pool-VOLs of RAID 5, RAID 6, and external volumes can coexist in the same pool. For pool-VOLs in the same pool:

• It is best practice to use RAID 6 for pool-VOLs, especially for a pool where the recovery time of a pool failure due to a drive failure is not acceptable.
• Pool-VOLs of different drive types with different RAID levels can coexist in the same pool. It is best practice to set one type of RAID level (the drive configurations such as 14D+2P) of parity groups on pool-VOLs. If you register pool-VOLs with multiple RAID levels to the same pool, the I/O performance depends on the RAID levels of pool-VOLs to be registered. In that case, note the I/O performance of the drives.

Data drive type

Caution:

• Pools should be built from pool-VOLs of the same capacity, type, and RAID level. If multiple pool-VOLs with different drive types are registered in the same pool, the I/O performance depends on the drive type of the pool-VOL to which the page is assigned. Therefore, if different drive types are registered in the same pool, ensure that the required I/O performance is not degraded by using less desirable drive types.
• If multiple data drives coexist in the same pool, avoid using data drives that are different capacities.

Internal volume: From 8 GB to 695 GB (from 9,676 cyl to 837,760 cyl).

External volume: From 8 GB to 927 GB (from 9,676 cyl to 1,117,760 cyl).

A volume whose capacity is less than 8 GB (9,676 cylinders) cannot be a pool volume.

If the pool-VOLs contain SSD parity groups, the pool must be configured 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, the following items must match:

• Drive type
• Drive capacity
• RAID level (the drive configurations such as 14D+2P) of parity groups
• 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.

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