User's Manual

78 Controllers
• Direct I/O —Specifies that reads are not buffered 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 also the default setting.
NOTE: Cache policy is not supported on any controller that does not have a battery.
Disk Cache Policy
Does my controller support this feature? See Supported Features .
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 can improve system performance.
The cache policies are:
• Enabled— Specifies that the disk cache policy is enabled.
•
Disabled— Specifies that the disk cache policy is disabled.
NOTE: For virtual disks based on SATA drives, the default Disk Cache Policy is
Enabled; and for virtual disks based on SAS drives, it is Disabled.
NOTE: For SAS 6i/R and PERC H200 family of controllers, disk cache policy setting
is available only after creating the virtual disk.
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 improves write performance. For
example, after the background initialization of a RAID 5 virtual disk
completes, the parity information has been initialized. After the background
initialization of a RAID 1 virtual disk completes, the physical disks are
mirrored.