Disk Array Unit Overview 1-7
Notes: A controller is called as HD (Host Director) in the
management software.
A logical disk configuring the RAID is called as LD (Logical Disk), and
the internal number of LD is called LDN (Logical Disk Number) in the
management software.
Initial Assignment Feature
You can assign a logical disk to the controller on the path to which you bound the
logical disk (built the RAID).
When an attempt is made to access the logical disk from the unassigned controller, the
error "illegal request - not assigned" is returned. When an attempt is made to unbind
this logical disk from the unassigned controller, the same error is returned. However, if
the ownership has been changed, the initial assignment feature is transferred to the
unassigned controller.
Auto Assignment Feature
The auto assignment feature allows you to access any logical disk in the subsystem
from the unassigned controller if the assigned controller is down. This feature is active
while the cross call is disabled.
When an I/O request to a logical disk not assigned to a DAU controller is received, the
system examines whether the adjacent controller is down. If the adjacent controller is
down, the system cancels assigning the logical disk to that controller and reestablishes
the assignment to the controller receiving the request. This reassignment is maintained
until the downed controller is operable, or a status change is received from management
software.
Even when the system in not equipped with the alternative auto assignment feature,
making the system recognize the logical disk again permits the access, allowing to
minimize the influence to the system operation. Figure 1-3 illustrates the Auto
assignment feature.
Figure 1-3. Auto Assignment Feature
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