Dell PowerVault MD3260i - Manual (Page 312)

Modification Priority
Modification priority defines the amount of system resources that are used when modifying virtual disk properties. If you
select the highest priority level, the virtual disk modification uses the most system resources, which decreases the
performance for host data transfers.
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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