User's Manual

Controllers 85
RAID Controller Read, Write, Cache, and Disk
Cache Policy
When creating a virtual disk, you specify the read, write, and cache policies
for the virtual disk. The following sub-section describes these policies.
NOTE: Read, write, and cache policies are not supported on the CERC SATA1.5/2s
controller.
Read Policy
Does my controller support this feature? See Supported Features
The read policies indicate whether or not the controller should read
sequential sectors of the virtual disk when seeking data.
• Read-Ahead —When using read-ahead policy, the controller reads
sequential sectors of the virtual disk when seeking data. Read-ahead policy
may improve system performance if the data is actually written to
sequential sectors of the virtual disk.
•
No-Read-Ahead —Selecting no-read-ahead policy indicates that the
controller should not use read-ahead policy.
•
Adaptive Read-Ahead —When using adaptive read-ahead policy, the
controller initiates read-ahead only if the two most recent read requests
accessed sequential sectors of the disk. If subsequent read requests access
random sectors of the disk, the controller reverts to no-read-ahead policy.
The controller continues to evaluate whether read requests are accessing
sequential sectors of the disk, and can initiate read-ahead if necessary.
•
Read Cache Enabled —When the read cache is enabled, the controller
reads the cache information to see if the requested data is available in the
cache before retrieving the data from the disk. Reading the cache
information first can provide faster read performance because the data (if
available in the cache) can more quickly be retrieved from the cache than
from the disk.
•
Read Cache Disabled —When the read cache is disabled, the controller
retrieves data directly from the disk and not from the cache.