Compaq HSZ80 manual Caching Techniques, Read Caching, Read-Ahead Caching, 20General Description

1–20General Description

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 also stores the data in its cache module. 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.

To set the maximum cache that can be transferred, see “SET unit-number”in Chapter 5, “CLI Commands.”

Read-Ahead Caching

Read-ahead caching begins once the controller has already processed a read request and it receives a sequential 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.