About releasing pages in a DP-VOL

Releasing pages in a DP-VOL frees up pool capacity. When a page in the DP-VOL contains zero data, the free capacity of a pool increases after the pages are released. You can reclaim zero pages on each V-VOL and then monitor the progress on the View Pool Management Status window. If you stop the reclaim zero pages operation, the zero pages that have already been reclaimed cannot be restored.

Logically, there is no difference between a page with zero data and the area of a DP-VOL without a page allotted. Both are effectively identical. However, a page with zero data uses pool capacity, whereas a DP-VOL without a page allotted does not use pool capacity.

Zero pages can be reclaimed when all the following conditions are satisfied:

  • The DP-VOL is not used in conjunction with another storage system software product that does not support reclaiming zero pages.

    See Using Dynamic Provisioning and Dynamic Tiering with other software products.

  • LDEV formatting is not being performed on the DP-VOL.
  • The DP-VOL is not blocked.
  • The DP-VOL does not have the data direct mapping attribute enabled.
  • The DP-VOL is not a deduplication system data volume.
  • The DP-VOL is associated with a pool.
  • The pool associated with the DP-VOL is not blocked, or is full and blocked.
  • The LUN path is not defined between DP-VOL and the host group enabled with host mode option 97.

Pages that include control cylinders are not processed when releasing pages in a DP-VOL.

Pages that include file system metadata cannot be reclaimed. Refer to Operating system and file system capacity for a table of the Pool Capacity Consumed by the file system.

While releasing pages from a DP-VOL, performance of the host I/O to the DP-VOL may temporarily decrease due to scanning for non-zero data.

If you stop an operation to reclaim zero pages in mid-stream, the pages that have been released will remain as free pool capacity.

After an operation to reclaim zero pages, Dynamic Provisioning automatically balances usage levels among parity groups in the pool. This rebalancing is performed on parity groups related to the pool. If you do not want automatic balancing of the usage levels of parity groups, call the Hitachi Solution Support Center to change your configuration.

NoteIf an operation to reclaim zero pages performs on pools comprised of pool volumes assigned by parity groups with accelerated compression enabled, the capacity reserved for writing data may not be reduced in comparison with the reduced pool capacity.

Dynamic Provisioning does not automatically balance the usage levels among parity groups if the cache memory is not redundant or if the pool usage reaches the threshold.

If all the tracks that belong to a page assigned to a DP-VOL have no records written, you can reclaim the page and return it to the pool's available capacity.

Caution

In the following cases, an operation of the reclaim zero pages stops and DP-VOL pages might not be released.

  • The pool-VOL accessed by the target DP-VOL is blocked.
  • The pool associated with the target DP-VOL is blocked while the operation to reclaim zero pages is in progress.
  • Cache memory failure occurs while the operation to reclaim zero pages is in progress.
  • While the operation to reclaim zero pages is in progress, the initial copy operation of the TrueCopy pair, the Universal Replicator pair, the global-active device pair, or the ShadowImage pair is performed on the DP-VOL.
  • The LUN path is defined between DP-VOL and the host group enabled with host mode option 97 while the operation to reclaim zero pages is in progress.
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