Dell PowerEdge Expandable RAID Controller 3 User Manual page 179

– In Write-back caching, the controller sends a data transfer
completion signal to the host when the controller cache has
received all the data in a transaction. This setting is not
recommended.
– In Write-through caching, the controller sends a data transfer
completion signal to the host when the disk subsystem has
received all the data in a transaction. This is the default setting for
cluster mode.
Write-through caching has a data security advantage over write-back
caching, whereas write-back caching has a performance advantage over
write-through caching.
Set the Read Policy.
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Read-ahead enables the SCSI read-ahead feature for the logical drive.
You can set this parameter to No-Read-Ahead, Read-ahead, or
Adaptive. Adaptive is the default setting.
– No-Read-Ahead specifies that the controller does not use read-
ahead for the current logical drive.
– Read-ahead specifies that the controller uses read-ahead for the
current logical drive.
– Adaptive specifies that the controller begins using read-ahead if
the two most recent disk accesses occurred in sequential sectors. If
all read requests are random, the algorithm reverts to No-Read-
Ahead, however, all requests are still evaluated for possible
sequential operation.
Set the Read Policy.
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Cache Policy applies to reads on a specific logical drive. It does not
affect the Read-ahead cache.
– Cached I/O specifies that all reads are buffered in cache memory.
– Direct I/O specifies that reads are not buffered in cache memory.
This is the default setting.
Direct I/O does not override the cache policy settings. Data is
transferred to cache and the host concurrently. If the same data block
is read again, it comes from cache memory.
Press <Esc> to exit the Advanced Menu.
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After you define the current logical drive, choose Accept and press
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<Enter>.
PERC 3 BI OS Confi gurat ion Uti lit y
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