Default Values For Segment Size And Cache Read Prefetch - IBM System Storage DS3000 Programming Manual

If the logical drive is for a single user with large I/O requests (such as multimedia), performance is
maximized when a single I/O request can be serviced with a single data stripe. A data stripe is the
segment size multiplied by the number of disk drives in the subsystem that are used for data storage. In
this environment, multiple disk drives are used for the same request, but each disk drive is accessed only
once.
The cacheReadPrefetch parameter turns on or turns off the ability of the controller to read additional
data blocks into the cache. When you turn on cache read prefetch, the controller copies additional data
blocks into the cache while it is reading requested data blocks from a disk drive into the cache. This
action increases the chance that a future request for data can be fulfilled from the cache, which improves
the speed with which data is accessed. The number of additional data blocks that the controller reads into
the cache is determined by the configuration settings for the storage subsystem that you use. Cache read
prefetch is important for applications that use sequential I/O, such as multimedia applications.
Valid values for the cacheReadPrefetch parameter are TRUE or FALSE. If you want to turn on cache read
prefetch, set the cacheReadPrefetch parameter to TRUE. If you want to turn off cache read prefetch, set the
cacheReadPrefetch parameter to FALSE.
The following table lists the default values for the segment size and cache read prefetch settings for
different storage subsystem uses.
Table 4-7. Default Values for Segment Size and Cache Read Prefetch
Storage Subsystem Use
File system
Database
Multimedia
After you have finished creating the subsystems and the logical drives by using the autoConfigure
storageSubsystem command, you can further define the properties of the logical drives in a configuration
by using the set logicalDrive command. (For a description about how to further define your
configuration, see "Modifying Your Configuration" on page 4-45.)
Security Type
The securityType parameter is used to specify the security subsystems with Full Disk Encryption (FDE)
drives. A Disk Encryption Activation premium feature must be purchased and enabled before you can
take advantage of the FDE drive security feature. The minimum version of controller firmware that
supports FDE Full Disk Encryption features is 07.5x.xx.xx. If this parameter is set to none, the created
subsystems and logical drives will not be encrypted. If the parameter is set to enabled, the subsystems
and logical drives will have security enabled and encrypted.
With FDE, the controller firmware can create a key and activate the Full Disk Encryption feature. The Full
Disk Encryption feature encrypts data as the data is written to the drive and decrypts the data as the
data is read from the drive. Without the key created by the controller, the data written to the drive is
inaccessible.
Before you can set the securityType parameter to capable or enabled, you must create a storage
subsystem security key. Use the create storageSubsystem securityKey command to create a storage
subsystem security key. These commands are related to the security key:
v create storageSubsystem securityKey
v set storageSubsystem securityKey
v import storageSubsystem securityKey
v export storageSubsystem securityKey
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IBM System Storage DS3000, DS4000, and DS5000: Command Line Interface and Script Commands Programming Guide
Segment Size (KB)
128
128
256
Cache Read Prefetch
TRUE
TRUE
TRUE