You can set up a disk group and create virtual
disks using the procedures in this section. Each procedure is explained
individually in this section in detail.
NOTE:When you use one physical disk group to create multiple virtual disks,
all the virtual disks must be configured with the same RAID level.
When you define the virtual disks,
you can set the following virtual disk parameters:
RAID level
Stripe element size
Read policy
Write policy
Type of initialization
Hot spare configuration
NOTE:The default hard drive
cache policy for a virtual disk with SAS hard drives is disabled, and
the cache policy for a virtual disk with SATA hard drives is enabled. The Virtual Disk parameter
cannot be changed in the BIOS Configuration Utility Ctrl R . Use Dell OpenManage Storage Management for the
hard drive cache setting operation.
The following
table shows the parameters that you can configure when defining virtual
disks.
Specifies whether the virtual disk
is RAID 0, 1, 5, 6, 10, 50, or 60. The number of disks, disk capacity,
requirements for fault tolerance, performance, and capacity should
be considered when selecting the RAID level.
Stripe Element Size
Specifies the size of the segments
written to each physical disk in a RAID 0, 1, 5, 6, 10, 50, and 60
virtual disk. You can set the stripe element size to 64 KB 128 KB,
256 KB, 512 KB, or 1 MB. 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
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 turned off and
then on, the controller may pause as the system flushes cache memory.
Controllers have 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.
Read Policy
Read-Ahead enables the read-ahead feature for the virtual disk. You can set
the parameter to Read-Ahead or No-Read-Ahead. The default is Read-Ahead.
Read-Ahead specifies that the controller uses Read-Ahead for the current virtual disk. Read-Ahead capability allows the controller to read sequentially
ahead of requested data and store the additional data in the cache
memory, anticipating that the data is required soon.
No-Read-Ahead specifies that the controller
does not use read ahead for the current virtual disk.
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