HP XP7 Storage - Manual (Page 7)

Behaviors Application
Cache Residency
◦
A parity group containing LDEVs assigned to Cache Residency cache areas
cannot be migrated to another CLPR.
◦
If Cache Residency cache area decreases the cache capacity of an existing
CLPR, adjust the cache capacity of the CLPR.
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. Continuous Access Journal
Calculating cache capacity
Before you partition cache memory into one or more CLPRs, calculate the cache capacity that you
need for the storage system. If necessary, install additional cache memory.
The recommended cache capacity is different for different system configurations. System differences
include:
•
Number of mounted MP blades
•
RAID level
•
Number of installed drives
•
Use of the following specialized applications: Thin Provisioning, Smart Tiers, Cache Residency,
Compatible XRC, or External Storage
Use this formula to calculate the recommended cache capacity for a CLPR:
Recommended cache capacity (GB) for a CLPR = (CLPR cap. (GB) –
ceil(Cache Residency extents (MB) / 2,048) × 2 GB)
Check the tables in the following sections for recommended CLPR cache capacity:
•
If you are using the storage system without Thin Provisioning, Smart Tiers, Cache Residency,
or Compatible XRC, see
“Cache capacity without specialized applications” (page 7) .
•
If you are using Thin Provisioning or Smart Tiers on the storage system, see “Cache capacity
with Thin Provisioning or Smart Tiers” (page 10) .
•
If you are using Cache Residency on the storage system, see “Cache capacity with Cache
Residency” (page 12) .
•
If you are using Compatible XRC on the storage system, see “Cache capacity with Compatible
XRC” (page 12) .
•
If you are using External Storage with the system, see “Cache capacity with External Storage”
(page 12) .
Cache capacity without specialized applications
Applications, such as Thin Provisioning, Smart Tiers, Cache Residency, or Compatible XRC require
more cache capacity to run. The recommended cache capacity is less for systems that do not use
specialized applications.
The next table lists the recommended cache capacity for storage systems that do not use performance
applications.
Recommended cache capacity for
a CLPR Number of MP blades Internal/external VOL for a CLPR (Total capacity)
8 GB 2 Less than 4 TB
12 GB 4
Calculating cache capacity 7