About decreasing pool capacity

When you want to decrease the capacity of, or shrink, a pool, you delete one or more pool volumes (pool-VOLs) by parity group from the pool. All of the used pages in the pool-VOL are moved to other pool-VOLs in the pool. If you delete the pool-VOL with the pool's system area, the used capacity and the management area are moved to other pool-VOLs in the pool.

For a pool that contains a V-VOL with the data direct mapping attribute disabled, if a pool-VOL is released after the pool shrinking, the released pool-VOLs (LDEVs) are blocked. Format the blocked pool-VOLs (LDEVs) before using them. If the blocked pool-VOL is an external volume, use Normal Format when formatting the volume. If the pool-VOL being deleted is an external volume and is disconnected during deletion, reconnect the external volume and then retry deleting the pool-VOL.

The more cache management devices for V-VOLs in the target pool, the more time is required for the pool shrinking to complete. At least 2 seconds are required for each cache management device. For more information about the number of cache management devices, see Cache management device requirements.

When pool shrinking is performed for some pool-VOLs in a parity group, SES(%) of raidcom get pool -key total_saving might display a hyphen (-) indicating that there is no saving effect.

You cannot perform the following operations on a pool while the shrink pool operation is in process. Wait until shrinking completes, or stop the shrinking process.

• Expand pools
• Shrink pools
• Edit pools
• Restore pools

• The pool shrinking cannot be performed while the following operations are performed on the target pool:
  • Create pools
  • Delete pools
  • Expand pools
  • Shrink pools
  • Restore pools
  • Stop the pool shrink operation
  • Change the threshold
  • Create V-VOLs
  • Expand V-VOLs

If the pool shrink operation is attempted while SOM 749 is set to ON, the processing stops abnormally.

If a blocked pool-VOL exists in the target pool, the pool capacity cannot be shrunk. Restore the blocked pool-VOL, and then shrink the pool capacity. Even if the pool-VOL in the pool is blocked, when the mapped capacity (MAPPED_PAGE_CAP(MB) for raidcom get ldev) of the pool-VOL is 0, the pool shrinking can be performed by using CCI (the pool-VOL can be removed from the pool).

If the pool shrinking is attempted while SOM 749 is set to ON, the processing stops abnormally. Before the pool shrinking, verify that the SOM 749 setting is OFF.

If you delete the pool-VOL with system area, a different system area pool-VOL will be assigned automatically according to the priority shown in the following table. If multiple pool-VOLs of the same drive type exist, the priority of each is determined by internal index of the storage system.