Hp XP P9500 Storage User Manual Page 117

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6. In the Confirm window, confirm the settings, in Task Name type a unique name for this task
or accept the default, and then click Apply.
If Go to tasks window for status is checked, the Tasks window opens.
About releasing pages in a THP V-VOL
Releasing pages in a THP V-VOL frees pool capacity. When all the pages in the THP V-VOL contain
zero data (no logical records), you can discard the zero data, and then release those pages.
Logically, there is no difference between a page with just zero data and the area of a THP V-VOL
without a page allotted. They are effectively identical. However, the former uses pool capacity
and the latter does not.
Zero data can be discarded when all the following conditions are satisfied:
The THP V-VOL is not used in conjunction with another P9500 product that does not support
discard zero data.
See “Using Thin Provisioning and Smart Tiers with other P9500 products” (page 68).
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.
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 discarding zero data in mid-stream, the pages that have been released will remain as
free pool capacity.
After the zero data is discarded and the pages are released, Thin Provisioning 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 the HP Technical Support to change your configuration.
Thin Provisioning does not automatically balance the usage levels among pool-VOLs if the cache
memory is not redundant or if the pool usage level exceeds the thresholds.
If all the data written to a page assigned to a THP V-VOL is binary zeroes, you can reclaim the
page and return it to the pool's available capacity.
If you have started a discard zero data operation, and the storage system losses power, which
then disrupts shared memory, the discard zero data operation will not automatically continue after
the storage system restarts.
In any of the following cases, discarding of zero data will stop, and THP V-VOL pages will not be
released.
LDEV formatting was performed while discarding zero data.
The pool-VOL that is being accessed by the target THP V-VOL was blocked.
The pool associated with the target THP V-VOL was blocked while discarding zero data.
Cache memory failure occurred while discarding zero data.
The THP V-VOL was released when zero data was discarded.
The initial copy operation between Continuous Access Synchronous pair or Continuous Access
Journal pair was performed on the THP V-VOL in which the zero data was discarded.
Managing pools and THP V-VOLs 117
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