Software Support

NOTE: Write-through is the default write policy setting when cluster mode is enabled.

• Write Cache Enabled Protected — The controller writes data to the write cache before writing data to the

physical disk. Because it takes less time to write data to the write cache than it does to a disk, enabling write

cache can improve system performance. After data is written to the write cache, the system is free to continue

with other operations. The controller, in the meantime, completes the write operation by writing the data from

the write cache to the physical disk. The Write Cache Enabled Protected policy is available only if the controller

has a functional battery. The presence of a functional battery ensures that data can be written from the write

cache to the physical disk even when there is power failure.

NOTE: Storage Management does not allow you to select the Write Cache Enabled Protected policy for

controllers that do not have a battery. This restriction protects a controller without a battery from the data

loss that may occur in the event of a power failure. When using the Create Virtual Disk Advanced Wizard

on a controller without a battery, the wizard either displays Write Cache Disabled as the only available

option or the wizard does not display any option for write policy.

• Write Cache Disabled — This is the only option available when the controller does not have a functional battery.

Cache Policy

Does my controller support this feature? See Supported Features.

The Direct I/O and Cache I/O policy apply to readings on a specific virtual disk. These settings do not affect the read-

ahead policy. The cache policies are:

• Cache I/O — Specifies that all reads are buffered in cache memory.

• 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 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.

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 cache policies are:

• Enabled — Disk Cache Policy is enabled.

• Disabled — Disk Cache Policy is disabled.

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.

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.