IBM System Storage DS3000, Руководство по программированию

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Cache Read Prefetch
The
cacheReadPrefetch
parameter enables the controller to copy additional data blocks into cache while
the controller reads and copies data blocks that are requested by the host from the disk drive 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 subsystem that you use determine the number of additional data blocks that the
controller 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 controller writes on a single disk drive
in a logical drive before writing data on the next disk drive. 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 controller at run time. If the value that you entered is not valid, the controller returns a
list of valid values. Using a single disk drive for a single request leaves other disk drives available to
simultaneously service other requests.
If the logical drive 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 disk drives in the subsystem
that are used for data transfers.) In this case, multiple disk drives are used for the same request, but each
disk drive 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 disk drives that are required to satisfy a data transfer request.
Set Logical Drive Attributes
This command defines the properties for a logical drive. You can use most parameters to define
properties for one or more logical drives. You also can use some parameters to define properties for only
one logical drive. The syntax definitions are separated to show which parameters apply to several logical
drives and which apply to only one logical drive.
Note: In configurations where subsystems consist of more than 32 logical drives, the operation can result
in host I/O errors or internal controller reboots due to the expiration of the timeout period before the
operation completes. If you experience host I/O errors or internal controller reboots, quiesce the host I/O
and try the operation again.
Syntax Applicable to One or More Logical Drives
set (allLogicalDrives | logicaldrive ["
logicaldriveName"] | logicaldrives ["logicaldriveName1" ... "logicaldriveNameN"] | logicaldrive <wwID>)
cacheFlushModifier=cacheFlushModifierValue
cacheWithoutBatteryEnabled=(TRUE | FALSE)
mediaScanEnabled=(TRUE | FALSE)
mirrorCacheEnabled=(TRUE | FALSE)
modificationPriority=(highest | high | medium | low | lowest)
owner=(a | b)
preReadRedundancyCheck=(TRUE | FALSE)
readCacheEnabled=(TRUE | FALSE)
writeCacheEnabled=(TRUE | FALSE)
cacheReadPrefetch=(TRUE | FALSE)
T10PIDisabled=(TRUE | FALSE)
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IBM System Storage DS3000, DS4000, and DS5000: Command Line Interface and Script Commands Programming Guide