Dell 38XX, 34XX, 32XX, 36XX manual Set Virtual Disk Copy, Cache Read Prefetch

Cache Read Prefetch

The cacheReadPrefetch parameter enables the RAID controller module to 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 disk into cache. This action increases the chance that a future request for data can be fulfilled from cache. Cache read prefetch 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.

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 stripe. (A data stripe is the segment size that is multiplied by the number of physical disks in the disk group that are used for data transfers.) In this case, multiple physical disks are used for the same request, but each physical disk is accessed only once.

For optimal performance in a multiuser database or file system storage environment, set your segment size to minimize the number of physical disks that are required to satisfy a data transfer request.

Set Virtual Disk Copy

Description

This command defines the properties for a virtual disk copy pair.

Syntax

set virtualDiskCopy target [targetName] [source [sourceName]]

copyPriority=(highest high medium low lowest) targetReadOnlyEnabled=(TRUE FALSE) copyType=(online offline)

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