LSI SCSI 320-0 Configuration page 79

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. The default stripe size is 64 MB.
A larger stripe size provides better read performance, especially if your computer does
mostly sequential reads. However, if you are sure that your computer does random read
requests more often, choose a small stripe size.
Write policy This parameter specifies the cache write policy. You can set the write
policy to Write-back or Write-through. The default is 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. If WriteBack is
enabled and the system is quickly turned off and then on, MegaRAID may hang when
flushing cache memory. Adapters that contain a battery backup will default to WriteBack
caching. Adapters which contain a battery will default to WriteBack.
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, whereas
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 parameter enables the SCSI read-ahead feature for the logical drive.
You can set this parameter to Normal, Read-ahead, or Adaptive. The default
setting is Normal.
Normal 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 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. The default setting is Direct I/O.
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. Press <Esc> to exit the
Advanced Menu.
Continued
Action
Chapter 4 MegaRAID Manager
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