In the following cases, an operation of the reclaim zero pages stops and DP-VOL pages might be not released.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 perform the operation to reclaim zero pages on each V-VOL and monitor progress. For details, see View Pool Management Status window. If you stop the operation to reclaim zero pages, the zero pages that have been reclaimed cannot be restored.
Logically, there is no difference between a page with just zero data and the area of a DP-VOL without a page allotted. Both are effectively identical. However, the former uses pool capacity and the latter does not.
Zero pages can be reclaimed when all the following conditions are satisfied:
The DP-VOL is not used in conjunction with another VSP G200, G400, G600 product which does not support reclaiming zero pages.
See Using Dynamic Provisioning or Dynamic Tiering with other VSP G200, G400, G600 products.
LDEV formatting is not being performed on the DP-VOL.
The DP-VOL is not blocked.
The DP-VOL is associated with a pool.
The pool associated with the DP-VOL is not blocked, or is full and blocked.
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 Data Systems customer support to change your configuration.
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 up to 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.
In the following cases, an operation of the reclaim zero pages stops and DP-VOL pages might be not 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, or the ShadowImage pair is performed on the DP-VOL.