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Parameter
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
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.
Security Type
The securityType parameter is valid for physical disks that are capable of selfencrypting disk (SED).
With SED, the RAID controller module firmware can create a key and activate the physical disk security
feature. The physical disk security feature encrypts data as the data is written to the physical disk and
decrypts the data as the data is read from the physical disk. Without the key created by the RAID
controller module, the data written to the physical disk is inaccessible.
Before you can set the securityType parameter to capable or enabled, you must create a storage array
security key. Use the create storageArray securityKey command to create a storage array
security key. The following commands are related to the security key:
Description
•
enabled—The disk group and virtual disks have security
enabled.
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