Users Guide
The Direct I/O and Cache I/O policy apply to readings on a specic virtual disk. These settings do not aect the read-ahead policy.
The cache policies are:
• Cache I/O — Species that all reads are buered in cache memory.
• Direct I/O — Species that reads are not buered in cache memory. When using Direct I/O, data is transferred to the controller
cache and the host system simultaneously during a read request. If a subsequent read request requires data from the same data
block, 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 rmware 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 rst 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
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