Dell PowerVault MD3060e Series Cli Manual Download Page 108

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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

•

set storageArray securityKey

•

start secureErase (physicalDisk | physicalDisks)

•

enable diskGroup [diskGroupName] security

Enclosure Loss Protection and Drawer Loss Protection

For enclosure loss protection to work, each physical disk in a disk group must be in a separate enclosure. If you set the

enclosureLossProtect

parameter to

TRUE

and have selected more than one physical disk from any one enclosure, the

storage array returns an error. If you set the

enclosureLossProtect

parameter to

FALSE

, the storage array performs

operations, but the disk group that you create might not have enclosure loss protection. Enclosure loss protection is not
valid when you create virtual disks on existing disk groups.
The

drawerLossProtect

parameter defines if data on a virtual disk is accessible if a drawer fails. When you assign the

physical disks, if you set the

drawerLossProtect

parameter to

TRUE

and select more than one physical disk from any

one drawer, the storage array returns an error. If you set the

drawerLossProtect

parameter to

FALSE

, the storage array