Dell 3 - Manual (Page 179)

PERC 3 BIOS Configuration Utility 177
– 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.
18 Set the Read Policy.
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.
19 Set the Read Policy.
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.
20 Press <Esc> to exit the Advanced Menu.
21 After you define the current logical drive, choose Accept and press
<Enter>.