HP XP P9500 Storage - Manual (Page 94)

Description Order in which pages are
allocated to tiers Tier of deleted pool-VOLs
If there is no free space in Tier 1 and Tier 2,
pages are allocated to Tier 3.
If there is free space in Tier 3, pages are
allocated to Tier 3. Tier 3, Tier 2, and Tier 1 Tier 3
If there is no free space in Tier 3, pages are
allocated to Tier 2.
If there is no free space in Tier 2 and Tier 3,
pages are allocated to Tier 1.
The following table describes page allocation in a 2-tier configuration.
Description Order in which pages are
allocated to tiers Tier of deleted pool-VOLs
If there is free space in Tier 1, pages are
allocated to Tier 1. Tier 1 and Tier 2 Tier 1
If there is no free space in Tier 1, pages are
allocated to Tier 2.
If there is free space in Tier 2, pages are
allocated to Tier 2. Tier 2 and Tier 1 Tier 2
If there is no free space in Tier 2, pages are
allocated to Tier 1.
Formatted pool capacity
The formatted pool capacity is the capacity of initialized free space in the pool, not the capacity
of all the free space in the pool. The free space of the pool is monitored by a storage system.
Space is formatted automatically if needed. You can confirm the formatted pool capacity in the
View Pool Management Status window (see
“View Pool Management Status window” (page 293) ).
Dependent on the load of the storage system, the format speed of the free space of the pool is
adjusted.
New pages are allocated, then initialized, during data write operations to the V-VOL. If a significant
number of new pages are allocated, initialization might be delayed as a result of conflicts between
data write and new page initialization processes. You can initialize the free space of a pool in
advance to prevent delays in data write operations.
If you want to change the method of performing the function to format the free space of a pool,
contact HP Technical Support.
Rebalancing the usage level among pool-VOLs
The usage level among pool-VOLs is rebalanced automatically so that the page usage ratio is
averaged across pool-VOLs and pool-VOL loads are distributed. When rebalancing is done on
jobs run for virtual volumes in the same pool, a page is reclaimed if all data on the page is zero.
The usage level among pool-VOLs is automatically rebalanced in the following cases:
•
Expanding pool capacity
•
Shrinking pool capacity
•
Reclaiming zero pages
•
Performing tier relocations several times
Performance of the host I/O may decrease due to movement of the existing data. If you do not
want to automate balancing of the usage level of pool-VOLs, call HP Technical Support. You can
94 Configuring thin provisioning