User's Manual

74 Controllers
Controller-supported RAID Levels
RAID controllers support different RAID levels. For information on which
RAID levels a controller supports, see the supported RAID levels section for
the controller in
Supported Features .
Controller-supported Stripe Sizes
When creating a virtual disk, you must specify the stripe size for the virtual
disk. Different controllers have different limitations on the stripe sizes they
can support. For information on the stripe sizes a controller supports, see the
virtual disk specifications section for the controller in
Supported Features .
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.
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.