HP StorageWorks XP Remote Web Console Software - Manual (Page 11)

Reclaiming Pages from a V-VOL
A V-VOL used as a migration target from a traditional nondynamic provisioned volume may have
large amounts of capacity dedicated to data that is all binary zeros. The XP Thin Provisioning pool
capacity used for the binary zero data written to the V-VOL can be reclaimed and returned as
available pool capacity. Capacity is provided to V-VOLs from the XP Thin Provisioning pool in
42-MB sized pages. Reclaiming capacity requires that these pages have only binary zero data
written to it. For instructions on how to reclaim pages containing binary zero data, see
“Releasing
Pages in a V-VOL” (page 71) .
Note that while releasing pages in a V-VOL, performance of host I/O to the V-VOL temporarily
decreases.
You cannot reclaim pages taken up by a V-VOL if any nonbinary zero data has been written to
them. In this case, the pages can be reclaimed only when the V-VOL is no longer needed and is
deleted.
If you perform the binary zero data discard operation, XP Thin Provisioning automatically rebalances
pool-VOL usage levels. If you do not want to automatically balance the usage levels of pool-VOLs,
consult HP technical support (see
“Calling HP Technical Support” (page 86) ).
XP Thin Provisioning Software automatically balances the usage levels among pool-VOLs in a pool
created with microcode version 60-05-0x or later. XP Thin Provisioning Software does not
automatically balance the usage levels among pool-VOLs if the cache memory is not redundant or
if the pool usage level is more than the pool thresholds.
V-VOL Management Table
Before you can use XP Thin Provisioning, a V-VOL management table is created. The V-VOL
management table associates V-VOLs (virtual volumes) with a pool. The V-VOL management table
is created automatically when the required additional shared memory is installed by your HP service
representative.
If data is lost from shared memory, the V-VOL management table will be restored using data stored
in reserved system areas inside the Pool. If this restore is unsuccessful, a stored copy of shared
memory will be copied from the SVP. This process is explained in
Table 2 (page 12) .
XP Thin Provisioning Components 11