IBM System Storage DS3000, Programming Manual

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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 drive for a single request leaves other 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 drives in the subsystem that
are used for data transfers.) In this case, multiple drives are used for the same request, but each 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 drives that are required to satisfy a data transfer request.
Related Topic
Naming Conventions
Set Logical Drive Attributes for a Disk Pool
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. Also, the syntax for logical drive mapping is listed
separately.
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, bring the host to a
quiescent state and try the operation again.
Syntax
set (allLogicalDrives | logicaldrive ["
logicaldriveName"] | logicaldrives ["logicaldriveName1" ... "logicaldriveNameN"] | logicaldrive <wwID>)
[(addCapacity = capacityValue[KB|MB|GB|TB|Bytes] |
[addDrives = (drive-spec-list)])|
cacheFlushModifier=cacheFlushModifierValue |
cacheReadPrefetch = (TRUE | FALSE) |
cacheWithoutBatteryEnabled=(TRUE | FALSE) |
mediaScanEnabled=(TRUE | FALSE) |
mirrorCacheEnabled=(TRUE | FALSE) |
modificationPriority=(highest | high | medium | low | lowest) | owner=(a | b) |
preReadRedundancyCheck = (TRUE | FALSE) |
readCacheEnabled=(TRUE | FALSE) |
redundancyCheckEnabled = (TRUE | FALSE) |
segmentSize = segmentSizeValue
userLabel = userlabelValue
writeCacheEnabled=(TRUE | FALSE) |
T10PIDisabled=(TRUE | FALSE)]
Parameters
Parameter Description
allLogicalDrives The properties for all logical drives in the storage
subsystem.
Chapter 3. Script Commands
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