IBM System Storage DS3000, Programming Manual

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Segment Size
The size of a segment determines how many data blocks that the controller writes on a single drive in a
logical drive before writing data on the next 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 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.
Cache Read Prefetch
Cache read prefetch lets the controller copy additional data blocks into cache while the controller reads
and copies data blocks that are requested by the host from the 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
.
Show storage subsystem Diagnostic Data Capture
This command show details of the Diagnostic Data Capture on the controller cache, if a Diagnostic Data
Capture is available.
Syntax
show storageArray coreDump
Parameters
None
Minimum Firmware Level
7.83
Show Storage Subsystem DBM Database
This command retrieves and shows metadata for the on-board backup locations of a storage subsystem.
When there are multiple backup locations, metadata is shown for each location.
Syntax
show storageSubsystem dbmDatabase
Parameters
None.
Chapter 3. Script Commands
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