Virtual disk write cache policies
The write cache policy of a virtual disk determines how the controller handles writes to the virtual disk.
Table 4. Write cache policies
Feature
Description
Write-Back
The controller sends a data transfer completion signal to the host
when the controller cache has received all the data in a transaction.
The controller then writes the cached data to the storage device in
the background.
NOTE:
The default cache setting for virtual disks is Write-
Back caching. Write-back caching is also supported for
single drive RAID 0 virtual disks.
Write-Through
The controller sends a data transfer completion signal to the host
system when the disk subsystem has received all the data in a
transaction.
All RAID volumes are presented as
Write-Through
to the operating
system (Windows and Linux) independent of the actual write cache
policy of the virtual disk. The PERC cards manage the data in cache
independently of the operating system or any applications.
NOTE:
Certain data patterns and configurations perform
better with a Write-Through cache policy.
NOTE:
Use the Dell OpenManage storage management application or the HII Configuration Utility to view and manage virtual
disk cache settings.
Conditions under which write-back is employed
Write-Back
caching is used under all conditions in which the battery is present and in good condition.
Conditions under which forced write-back with no battery is employed
CAUTION:
It is recommended that you use a power backup system when forcing Write-Back to ensure there is no loss of data if
the system suddenly loses power.
Write-Back
mode is available when you select
Force WB with no battery
. When
Forced Write-Back
mode is selected, the virtual disk is in
Write-Back
mode even if the battery is not present.
Virtual disk read cache policies
The read policy of a virtual disk determines how the controller handles reads to that virtual disk.
20
Features
