Conditions Under Which Forced Write-Back With No Battery Is Employed; Virtual Disk Read Cache Policies; Reconfiguration Of Virtual Disks - Dell PowerEdge H730P User Manual

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. The read
policies are:
Always Read Allows the controller to read sequentially ahead of requested data and to store the
Ahead additional data in cache memory, anticipating that the data is required soon. This
speeds up reads for sequential data, but there is little improvement when accessing
random data.
No Read Ahead Disables the Read-Ahead capability.

Reconfiguration Of Virtual Disks

An online virtual disk can be reconfigured in ways that expands its capacity and/or change its RAID level.
NOTE: Spanned virtual disks such as RAID 10, 50, and 60 cannot be reconfigured.
NOTE: Reconfiguring Virtual Disks typically impacts disk performance until the reconfiguration
operation is complete.
Online Capacity Expansion (OCE) can be done in two ways:
• 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 a virtual disk is created and it does not use the maximum size of the disk group, free space is
available.
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 not required. The source RAID level
column indicates the virtual disk RAID level before the RLM/OCE operation and the target RAID level
column indicates the RAID level after the RLM/OCE operation.
NOTE: If the controller already contains the maximum number of virtual disks, you cannot perform
a RAID level migration or capacity expansion on any virtual disk.
NOTE: The controller changes the write cache policy of all virtual disks undergoing a RLM/OCE
operation to Write-Through until the RLM/OCE operation is complete.
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