Dell PowerVault MD3260i - Manual (Page 159)

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.
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:
• create storageArray securityKey
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