Hp StorageWorks 2000 Family Modular Smart Array CLI reference guide (481600-002, May 2008)

112 HP StorageWorks 2000 Family Modular Smart Array CLI reference guide • May 2008
Independent Cache Performance Mode
In the storage system’s default operating mode, Active-Active, data for volumes
configured to use write-back cache is automatically mirrored between the two
controllers. Cache redundancy has a slight impact on performance but provides fault
tolerance. You can disable cache redundancy, which permits independent cache
operation for each controller; this is called independent cache performance mode
(ICPM).
The advantage of ICPM is that the two controllers can achieve very high write
bandwidth and still use write-back caching. User data is still safely stored in
nonvolatile RAM, with backup power provided by super-capacitors should a power
failure occur. This feature is useful for high-performance applications that do not
require a fault-tolerant environment for operation; that is, where speed is more
important than the possibility of data loss due to a drive fault prior to a write
completion.
The disadvantage of ICPM is that if a controller fails, the other controller will not
be able to fail over (that is, take over I/O processing for the failed controller). If a
controller experienced a complete hardware failure, and needed to be replaced, then
user data in its write-back cache is lost.
Caution – Data might be compromised if a RAID controller failure occurs after it
has accepted write data, but before that data has reached the disk drives. Do not use
ICPM in an environment that requires fault tolerance.
Note – Independent cache performance mode disables partner firmware upgrade.
Controllers must be upgraded manually.
The operating mode applies per storage system, not per volume.
Input
To set cache options for a volume:
set cache-parameters volume [write-policy write-back|
write-through] [optimization standard|super-sequential]
[read-ahead-size disable|default|maximum|64KB|128KB|256KB|512KB|
1MB|2MB|4MB|8MB|16MB|32MB]