A-11
Theory of Controller Operation
Active-Passive Mode
In active-passive mode, there is one active and one passive RAID
controller. The primary (active) controller operates with both of its
host ports enabled and presents all LUNs on both ports to
maximize bandwidth. The secondary (passive) controller keeps
both of its host ports passive, and does not service any LUNs. Both
controllers monitor each other’s heartbeats and the passive
controller receives write data and parity logs from the active
controller.
If the active controller fails, normal fail-over occurs to the passive
controller, which becomes active by enabling both of its host ports
and takes ownership of all arrays.
Controller 1 is the default active controller. Controller 2 is always
passive unless controller 1 fails. The default active controller is not
selectable.
Because the active controller does not have to mirror the passive
controllers data, more write-back cache memory can be made
available to the active controller. This means that half the cache
memory can be dedicated to writes and half to reads. This is the
same allocation used in stand-alone mode.
Table A-4 Presentation of LUNs in Active-Passive Mode
Controller
Status
Controller 1
Host Port 0
(FC1)
Controller 1
Host Port 1
(FC2)
Controller 2
Host Port 0
(FC1)
Controller 2
Host Port 1
(FC2)
Both
controllers
online
Controller 1
LUNs
Inactive
Inactive
Controller 2
LUNs
Controller 1
failed
Inactive
Inactive
Controller 1
LUNs
Controller 2
LUNs
Controller 2
failed
Controller 1
LUNs
Controller 2
LUNs
Inactive
Inactive
DuraStor IUG - Online.book Page 11 Friday, July 19, 2002 3:06 PM
