Rebalancing the usage level among parity groups

If multiple parity groups that contain LDEVs used as pool volumes exist, rebalancing can improve biased usage rates in parity groups. Rebalancing is performed as if each parity group were a single pool volume. After rebalancing, the usage rates of LDEVs in a parity group may not be balanced, but the usage rate in the entire pool is balanced.

The usage level among parity groups is automatically rebalanced when these operations are in progress:

NoteIn pools comprised of pool volumes assigned by parity groups with accelerated compression enabled, the rebalancing operation is performed with consideration of the parity group's used capacity. Therefore, after performing the rebalancing operation, the capacity of the pool volume may not be reduced.

  • Expanding pool capacity
  • Shrinking pool capacity
  • Reclaiming zero pages
  • Reclaiming zero pages in a page release request issued by the host with the Write Same command, for example.
  • Performing tier relocations

If you expand the pool capacity, Dynamic Provisioning moves data to the added space on a per-page basis. When the data is moved, the usage rate among parity groups of the pool volumes is rebalanced.

Host I/O performance may decrease when data is moved. If you do not want to have the usage level of parity groups automatically balanced, call the customer support.

You can see the rebalancing progress of the usage level among parity groups in the View Pool Management Status window. Dynamic Provisioning automatically stops balancing the usage levels among parity groups if the cache memory is not redundant or the pool usage rate reaches up to the threshold.

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