Cache Partitioning Rules And Guidelines - HP StorageWorks P9000 - Disk Arrays User Manual

After installing and partitioning cache memory in one or more CLPRs, you may want to use Cache
Residency software to manage your cache. For more information, see the HP StorageWorks P9000
Performance for Open and Mainframe Systems User Guide.

Cache partitioning rules and guidelines

Observe the following rules, restrictions, and guidelines when creating cache logical partitions:
Rules
To create cache partitioning, enable Cache partition on your system.
CLPR0 is the default CLPR in a storage system. If you have not yet created any cache logical
partitions, all cache belongs to CLPR0.
Usually, you can create a CLPR if the subsystem has 4 GB cache. However, when creating a
CLPR while using Cache Residency, the remaining cache size, which is calculated by subtracting
Cache Residency size from the cache size of CLPR0, must be 8 GB or more.
Adding or changing CLPR definitions or configurations may take hours to implement and
cannot be canceled or modified until all changes are complete. For assistance or for more
information, contact your HP account team.
Restrictions
The following operations are not allowed when multiple CLPRs are involved:
Creating LUSE volumes across multiple CLPRs. If you forcibly perform this operation and create
a LUSE across multiple CLPRs, the LUSE volumes cannot be used for Continuous Access
Synchronous or Continuous Access Synchronous Z pair volumes.
Business Copy Quick Restore operations that affect multiple CLPRs.
Auto LUN manual migration operations that affect multiple CLPRs.
A parity group containing LDEVs assigned to Cache Residency cache extents (cache areas)
cannot be migrated to another CLPR. See the HP StorageWorks P9000 Performance for Open
and Mainframe Systems User Guide for more information about cache extents.
If you are using Continuous Access Journal, Continuous Access Journal data volumes and
journal volumes can belong to different CLPRs. All journal volumes in the same journal must
belong to the same CLPR. If not, an error occurs.
Guidelines
Install any needed additional cache memory before partitioning cache. It will be difficult to
add additional cache memory after partitioning cache into CLPRs.
If the cache capacity of defined CLPR is decreased by the Cache Residency cache area, cancel
the setting of bind mode or priority mode of Cache Residency, change the cache capacity of
CLPR, and then set the bind mode or priority mode again.
When the Cache Residency is used with CLPR, HP recommends that you decide the remaining
cache capacity of each CLPR after subtraction of cache capacity for Cache Residency according
to Table 1 (page
Best practice is to create cache logical partitions either during the initial installation and setup
or during a maintenance window, because cache logical partition operations can significantly
degrade host performance. If you must perform such operations on a production machine,
use Performance Monitor to verify that the write pending rate, including spikes, is well below
30%. See the HP StorageWorks P9000 Performance for Open and Mainframe Systems User
Guide for more information.
6 Creating virtual cache partitions
5).