Avago Technologies MegaRAID SATA 150-4 (523) - Manual (Page 69)

Detailed Configuration Instructions 3-21
Version 2.0 Copyright © 2003–2006 by LSI Logic Corporation. All rights reserved.
Table 3.10 Logical Drive Parameters and Descriptions
Parameter Description
RAID Level The number of physical drives in a specific array determines the RAID levels that can
be implemented with the array.
Stripe Size The stripe size parameter specifies the size of the segments written to each disk in
a RAID 1, 5, 10, or 50 configuration. You can set the stripe size as 8, 16, 32, 64, or
128 Kbytes. The default is 64 Kbytes.
A larger stripe size produces higher read performance, especially if your computer
does mostly sequential reads. If your computer regularly performs random read
requests, select a smaller stripe size.
Write Policy Write Policy specifies the cache write parameter. You can set the write policy 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. LSI
recommends using this setting in standard mode.
Note: If Write-back is enabled and the system is quickly turned off and on,
the RAID controller may hang when flushing cache memory.
Controllers that contain a battery backup default to Write-back
caching.
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.
Write-through caching has a data security advantage over write-back caching, while
write-back caching has a performance advantage.
Note: Enabling clustering turns off write cache. The MegaRAID 320-2
controller supports clustering.
Read Policy The read parameter determines the type of read option for the logical drive. You can
set this parameter to Normal, Read-ahead, or Adaptive. The default setting is Normal.
The options are
•
Normal specifies that the controller reads only the requested data and does not
read ahead for the current logical drive.
•
Read-ahead specifies that the controller uses read-ahead for the current logical
drive. Read-ahead capability allows the adapter to read sequentially ahead of
requested data and store the additional data in cache memory, anticipating that
the data is needed soon. Read-ahead supplies sequential data faster, but is not
as effective when accessing random data.
•
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.