Users Guide

it can be read directly from the controller cache. The Direct I/O setting does not override the cache policy settings. Direct I/O is the
default setting.
NOTE: Cache policy is not supported on controllers that do not have a battery.
Disk Cache Policy
Does my controller support this feature? See Supported Features.
NOTE: The Disk Cache Policy feature is not supported on solid-state disks (SSDs) and on SAS 12 Gbps Adapter.
The Disk Cache Policy feature is supported on Non-RAID SAS/SATA physical disks (HDDs) connected to PERC hardware controllers and
on RAID SAS/SATA physical disks connected to Software RAID S130 controller. This feature is not dependent on the controller mode and
can function as usual when the controller is running in RAID or HBA mode.
Set the physical disk caching policy of all members of a virtual disk by enabling the Disk Cache Policy. When this feature is enabled, the
physical disk writes data to the physical disk cache before writing it to the physical disk. Because it is faster to write data to the cache
than to a disk, enabling this feature improves system performance.
The following are the disk cache policy options for Non-RAID disks connected to a PERC hardware controller:
• Enabled — Disk Cache Policy is enabled.
• Disabled — Disk Cache Policy is disabled.
• Unchanged — The disk uses the default write cache mode.
NOTE: The Unchanged option is applicable only for PERC 9 hardware controllers with the latest firmware version.
NOTE: If you want to revert the Disk Cache Policy settings of the physical disks to the factory default settings, then
you must restart the server.
The following are the disk cache policy options for RAID disks connected to Software RAID S130 controller:
• Default — The disk uses the default write cache mode.
• Enabled — Disk Cache Policy is enabled.
• Disabled — Disk Cache Policy is disabled.
• Inconsistent — The disk cache policy is not uniform across all the physical disks in the virtual disk. For example, if a virtual disk
contains three physical disks; the disk cache policy of the first physical disk is Enabled, the second physical disk is Disabled, and the
third physical disk is Default. Then the disk cache policy state for the virtual disk is displayed as Inconsistent.
NOTE:
The default setting for Disk Cache Policy for virtual disks based on SATA drives is Enabled, and for virtual disks
based on SAS drives is Disabled.
NOTE: For SAS 6i/R and PERC H200 family of controllers, the Disk Cache Policy setting is available only after creating
the virtual disk.
Related Task
• Changing The Virtual Disk Policy
Background Initialization On PERC Controllers
On PERC controllers, background initialization of a redundant virtual disk begins automatically within 0 to 5 minutes after the virtual disk is
created. The background initialization of a redundant virtual disk prepares the virtual disk to maintain redundant data and improve write
performance. For example, after the background initialization of a RAID 5 virtual disk completes, the parity information is initialized. After
the background initialization of a RAID 1 virtual disk completes, the physical disks are mirrored.
The background initialization process helps the controller identify and correct problems that may occur with the redundant data later. In
this regard, the background initialization process is similar to a check consistency.
The background initialization should be allowed to run to completion. If canceled, the background initialization automatically restarts within
0 to 5 minutes. Some processes such as read and write operations are possible while the background initialization is running. However,
other processes such as creating a virtual disk, cannot be run concurrently with background initialization. These processes cause the
background initialization to cancel.
Related concepts
Canceling Background Initialization
Controllers
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