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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. The read policies are:
•
Always Read Ahead
—
A
llows the controller to read sequentially ahead of
requested data and to store the additional data in cache memory,
anticipating that the data is required soon. This speeds up reads for
sequential data, but there is little improvement when accessing random
data.
•
No Read Ahead
—Disables the
Read-Ahead
capability.
•
Adaptive Read Ahead
—Begins using
Read-Ahead
if the two most recent
disk accesses occurred in sequential sectors. If the read requests are
random, the controller reverts to
No Read Ahead
mode.
NOTE: The default read cache setting for virtual disks is Adaptive Read Ahead.