HP StorageWorks 2000 Modular Smart Array Reference Guide (481599-003, August 2008)

90 HP StorageWorks 2000 Family Modular Smart Array reference guide • August 2008
3. Select the standard, snap-pool, or master volume whose cache settings you want to
change.
4. Set Read Ahead Size to one of the following options:
■ Default – Sets one chunk for the first access in a sequential read and one stripe
for all subsequent accesses. The size of the chunk is based on the chunk size used
when you created the virtual disk (the default is 64 KB). Non-RAID and RAID 1
virtual disks are considered to have a stripe size of 64 KB.
■ Disabled – Turns off read-ahead cache. This is useful if the host is triggering read
ahead for what are random accesses. This can happen if the host breaks up the
random I/O into two smaller reads, triggering read ahead. You can use the
volume statistics read histogram to determine what size accesses the host is
doing.
■ 64, 128, 256, or 512 KB; 1, 2, 4, 8, 16, or 32 MB – Sets the amount of data to
read first, and the same amount is read for all read-ahead accesses.
■ Maximum – Lets the controller dynamically calculate the maximum read-ahead
cache size for the volume. For example, if a single volume exists, this setting
enables the controller to use nearly half the memory for read-ahead cache.
Note – Only use Maximum when disk drive latencies must be absorbed by cache.
5. Set Cache Optimization to one of the following options:
■ Standard – Works well for typical applications where accesses are a combination
of sequential and random. This method is the default.
■ Super-Sequential – Slightly modifies the controller’s standard read-ahead caching
algorithm by enabling the controller to discard cache contents that have been
accessed by the host, making more room for read-ahead data. This setting is not
optimal if random accesses occur; use it only if your application is strictly
sequential and requires extremely low latency.
6. Click Set Read Ahead Cache Options.
When processing is complete, the new setting is displayed in the Volume Menu
panel.