Specifications

2–9
Compaq HSG80 Array Controller ACS Version 8.4 Configuration and CLI Reference Guide
Caching Techniques
The cache module supports the following caching techniques to increase the
subsystem’s read and write performance:
■ Read caching
■ Read-ahead caching
■ Write-through caching
■ Write-back caching
Read Caching
When the controller receives a read request from the host, it reads the data from the
disk drives, delivers it to the host, and stores the data in its cache module. Subsequent
reads for the same data will take the data from cache rather than accessing the data
from the disks. This process is called read caching.
Read caching can decrease the subsystem’s response time to many of the host’s read
requests. If the host requests some or all of the cached data, the controller satisfies the
request from its cache module rather than from the disk drives. By default, read
caching is enabled for all storage units.
See “ADD UNIT,” page 7–27, for information on the switch,
MAXIMUM_CACHED_TRANSFER.
Read-Ahead Caching
Read-ahead caching begins when the controller has already processed a read request,
and it receives a subsequent read request from the host. If the controller does not find
the data in the cache memory, it reads the data from the disks and sends it to the cache
memory.