Chapter 9. Administration - Logical Tab
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cache read prefetch and the segment size. Table 9-1 shows the defaults predefined for
each I/O type.
Table 9-1 Logical drive defaults I/O characteristics
b. The segment size is chosen according to the usage pattern. For custom settings, you
can directly define the segment size.
c. Dynamic cache read prefetch is important for multimedia applications that use
sequential I/O, by allowing the controller, while it is reading and copying host-requested
data blocks from disk, to copy additional data blocks into the cache.
d. The preferred controller handles the logical drive normally if both controllers and I/O
paths are online. You can distribute your logical drives between both controllers to
provide better load balancing between them. The default is to alternate the logical
drives on the two controllers.
It is better to spread the logical drives by the load that they cause on the controller. If
you do not know the expected access pattern for each logical drive, you can evaluate it
by using the performance monitor option integrated with the Storage Manager. Based
on data gathered from the Performance Monitor, move some logical drives to the other
preferred controller to balance the load if required (see Chapter 3, “IBM System
Storage DS3500 Storage System planning tasks” on page 29 for more information.
5. Click Next, and the Specify Logical Drive-to-LUN Mapping window (Figure 9-20 on
page 242) opens. This window allows you to choose between mapping your created
logical drive to the default host group or to “Map later using the Mappings View.” If you
choose the “Default mapping”, then your new logical drive is mapped to the Default Group
I/O type
File system
Database
Multimedia
Segment size
128 K
128 K
256 K
Modification priority
High
High
High
Read cache
Enable
Enable
Enable
Write cache
Enable
Enable
Enable
Write cache without
batteries
Disable
Disable
Disable
Write cache with
mirroring
Enable
Enable
Enable
Flush write cache after
10 seconds
10 seconds
10 seconds
Dynamic cache
prefetch
Enable
Enabled
Enable
Enable background
media scan
Enable
Enable
Enable
Media scan with
redundancy check
Disable
Disable
Disable
Pre-read redundancy
check
Disabled
Disabled
Disabled
Note: The recommended settings values for creating volumes are default settings:
dynamic cache read prefetch enabled for all RAID types, and the segment size 128
kB.
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