Users Guide

NOTE: Use the Dell OpenManage storage management application or the HII Conguration Utility to view and manage virtual
disk cache settings.
Conditions under which write-back is employed
Write-Back caching is used under all conditions in which the battery is present and in good condition.
Conditions under which forced write-back with no battery is
employed
CAUTION: It is recommended that you use a power backup system when forcing Write-Back to ensure there is no loss of data if
the system suddenly loses power.
Write-Back mode is available when you select Force WB with no battery. When Forced Write-Back mode is selected, the virtual disk is in
Write-Back mode even if the battery is not present.
Virtual disk read cache policies
The read policy of a virtual disk determines how the controller handles reads to that virtual disk.
Table 4. Read policies
Feature Description
Read Ahead
Allows the controller to read sequentially ahead of requested data
and to store the additional data in cache memory, anticipating that
the data is required soon. This speeds up reads for sequential data,
but there is slight improvement when accessing random data.
No Read Ahead
Disables the Read Ahead capability.
Adaptive Read Ahead
Adaptive read ahead is no longer supported. Selecting adaptive read
ahead is equivalent to selecting Read Ahead option.
Reconguration of virtual disks
An online virtual disk can be recongured in ways that expands its capacity and/or change its RAID level.
NOTE
: Spanned virtual disks such as RAID 50 and 60 cannot be recongured.
NOTE: Reconguring Virtual Disks typically impacts disk performance until the reconguration operation is complete.
Online Capacity Expansion (OCE) can be done in two ways:
1 If there is a single virtual disk in a disk group and free space is available, the virtual disk’s capacity can be expanded within that free
space. If multiple virtual disks exist within a common disk group, those virtual disk’s capacities cannot be expanded.
NOTE
: Online Expansion Capacity is allowed on a disk group with a single virtual disk that begins at the start of the
physical disk. It is not allowed when there is a free space at the beginning of a disk.
2 Free space is also available when a disk group’s physical disks are replaced by larger disks using the Replace Member feature. A virtual
disk's capacity can also be expanded by performing an OCE operation to add more physical disks.
RAID Level Migration (RLM) refers to changing a virtual disk’s RAID level. Both RLM and OCE can be done at the same time so that a
virtual disk can simultaneously have its RAID level changed and its capacity increased. When a RLM/OCE operation is complete, a reboot is
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Features