Dell 34XX, 38XX, 32XX, 36XX manual Additional Information, Cache Read Prefetch

Parameter	Description
	• capable—The disk group and virtual disks are capable of
	having security set, but security has not been enabled.
	• enabled—The disk group and virtual disks have security
	enabled.
dataAssurance	The setting to specify that a disk group, and the virtual disks
	within the disk group, has data assurance protection to make
	sure that the data maintains its integrity. When you use this
	parameter, only protected physical disks can be used for the disk
	group. These settings are valid:
	• none - The disk group does not have data assurance
	protection.
	• enabled - The disk group has data assurance protection. The
	disk group supports protected information and is formatted
	with protection information enabled.

Additional Information

Cache Read Prefetch

The cacheReadPrefetch command lets the RAID controller module copy additional data blocks into cache while the RAID controller module reads and copies data blocks that are requested by the host from the physical disks into cache. This action increases the chance that a future request for data can be fulfilled from cache. CacheReadPrefetch is important for multimedia applications that use sequential data transfers. The configuration settings for the storage array that you use determine the number of additional data blocks that the RAID controller module reads into cache. Valid values for the cacheReadPrefetch parameter are TRUE or FALSE.

You do not need to enter a value for the cacheReadPrefetch parameter or the segmentSize parameter. If you do not enter a value, the RAID controller module firmware uses the usageHint parameter with fileSystem as the default value. Entering a value for the usageHint parameter and a value for the cacheReadPrefetch parameter or a value for the segmentSize parameter does not cause an error. The value that you enter for the cacheReadPrefetch parameter or the segmentSize parameter takes priority over the value for the usageHint parameter.

Segment Size

The size of a segment determines how many data blocks that the RAID controller module writes on a single physical disk in a virtual disk before writing data on the next physical disk. Each data block stores 512 bytes of data. A data block is the smallest unit of storage. The size of a segment determines how many data blocks that it contains. For example, an 8 KB segment holds 16 data blocks. A 64 KB segment holds 128 data blocks.

When you enter a value for the segment size, the value is checked against the supported values that are provided by the RAID controller module at run time. If the value that you entered is not valid, the RAID controller module returns a list of valid values. Using a single physical disk for a single request leaves other physical disks available to simultaneously service other requests.

If the virtual disk is in an environment where a single user is transferring large units of data (such as multimedia), performance is maximized when a single data transfer request is serviced with a single data

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