HP XP P9000 Provisioning for Mainframe Systems User Guide

Zero pages can be reclaimed when all the following conditions are satisfied:
• The THP V-VOL is not used in conjunction with another P9500 product which does not support
reclaiming zero pages.
See “Using Thin Provisioning Z or Smart Tiers Z with other P9500 products” (page 59).
• LDEV formatting is not being performed on the THP V-VOL.
• The THP V-VOL is not blocked.
• The THP V-VOL is associated with a pool.
• The pool associated with the THP V-VOL is not blocked, or is full and blocked.
• The THP V-VOL is not TSE-VOL.
Pages that include control cylinders are not processed when releasing pages in a THP V-VOL.
While releasing pages from a THP V-VOL, performance of the host I/O to the THP V-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, Thin Provisioning Z automatically balances usage levels
among pool-VOLs in the pool. This rebalancing is performed on all of the THP V-VOLs and pool-VOLs
in the pool. If you do not want automatic balancing of the usage levels of pool-VOLs, call HP
Technical Support to change your configuration.
Thin Provisioning Z does not automatically balance the usage levels among pool-VOLs 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 THP V-VOL have no records written, you can
reclaim the page and return it to the pool's available capacity.
If you have started an operation to reclaim zero pages, and the storage system loses power, the
shared memory is disrupted. The operation does not automatically continue after the storage system
restarts.
In the following cases, an operation reclaim zero pages stops and THP V-VOL pages are not
released.
• LDEV formatting is performed while the operation to reclaim zero pages is in progress.
• The pool-VOL accessed by the target THP V-VOL is blocked.
• The pool associated with the target THP V-VOL is blocked while the operation to reclaim zero
pages is in progress.
• Cache memory failure occurs the operation to reclaim zero pages is in progress.
• The THP V-VOL is released when the operation to reclaim zero pages is in progress.
• The initial copy operation between Continuous Access Synchronous Z pair, Continuous Access
Journal Z, Business Copy pair is performed on the THP V-VOL in which the zero pages are
reclaimed.
Releasing pages in a THP V-VOL
You can reclaim pages in a THP V-VOL to free pool capacity. If a page assigned to a THP V-VOL
contains no logical records, you can reclaim the page. Before releasing pages in a THP V-VOL,
see “About releasing pages in a THP V-VOL” (page 130)).
Managing pools and THP V-VOLs 131