LSI SCSI 320-0 Configuration page 29

Using Easy Configuration,
Step
6 Set the stripe size, cache write policy, Read policy, and I/O (cache) policy from the
Advanced Menu.
Stripe size This parameter specifies the size of the segments written to each disk in a
RAID 1, 3, 5, 10, 30, or 50 logical drive. You can set the stripe size to 2 KB, 4 KB, 8 KB,
16 KB, 32 KB, 64 KB, or 128 KB. A larger stripe size produces better read performance,
especially if your computer does mostly sequential reads. If you are sure that your
computer does random read requests more often, choose a small stripe size. The default is
64 KB.
Write Policy This option sets the caching method to write-back or write-through.
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.
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.
Write-through caching has a data security advantage over write-back caching. Write-back
caching has a performance advantage over write-through caching. You should not use
write-back for any logical drive that is to be used as a Novell NetWare volume.
Read-ahead This option enables the SCSI read-ahead feature for the logical drive. You
can set this parameter to Normal, Read-ahead, or Adaptive.
Normal specifies that the controller does not use read-ahead for the current logical drive.
This is the default setting.
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 Normal; however, all requests are still evaluated for possible sequential
operation.
Cache Policy This parameter 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. 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. This is the default
setting.
Press <Esc> to exit the Advanced Menu.
Continued
Action
Chapter 2 MegaRAID Configuration Utility
Cont'd
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