Dell 6 series, User Manual

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Configuring and Managing RAID
Table 6-2 shows the parameters that you can configure when defining
virtual disks.
Table 6-2. Virtual Disk Parameters and Descriptions
Parameter Description
RAID Level RAID Level specifies whether the virtual disk is RAID 0, 1, 5,
6, 10, 50, or 60. The RAID level you select depends on the
number of disks, disk capacity, and the requirements for fault
tolerance and performance. More more information, see
"Summary of RAID Levels" on page 17.
Stripe Element Size Stripe Element Size specifies the size of the segments written
to each physical disk in a RAID 0, 1, 5, 6, 10, and 50
virtual disk. You can set the stripe element size to
8 KB , 16 KB ,
32 KB , 64 KB , 128 KB , 256 KB , 512 KB , or 1024 KB . The
default and recommended stripe element size is 64 KB .
A larger stripe element size provides better read performance if
your system mostly does sequential reads.
Write Policy Write Policy specifies the controller write policy. 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.
NOTE:
If a Battery Backup Unit (BBU) is present, the default
cache setting is Write-Back . If no BBU is present, the default
cache policy default setting is Write-Through .
NOTE:
If Write-Back is enabled and the system is quickly turned
off and then on, the controller may pause as the system flushes
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-Back caching has a performance advantage over
Write-Through caching.
NOTE:
Certain data patterns and configurations perform better
with Write-Through cache policy.
Dell_PERC6.2_UG.book Page 84 Wednesday, June 24, 2009 6:08 PM