Changing the Write Policy
When you configure a
logical drive, the ServeRAID controller sets the write policy
to write-through (WT) mode, where the completion status
of a write command is sent after the data is written to the
hard disk drive. Under certain workloads, you can improve
performance by changing the write policy to write-back
(WB) mode, where the completion status is sent after the
data is copied to cache memory, but before the data is
actually written to the storage device.
Although you might gain performance with write-back
mode, it creates a greater risk of losing data due to a
power failure. If a ServeRAID controller failure occurs
while data is in the cache the data is lost. This is because
the system gets a completion status message when the
data reaches cache memory, but before data is actually
written to the hard disk drive.
To change the write policy:
A screen similar to the following appears.
If you change the write policy to WB, wait at least
10 seconds after the last operation before you turn off the system. It takes that
long for the system to move the data from the cache memory to the storage device.
Failure to follow this practice can result in data loss.
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