Adaptec 412R User Guide - Page 113

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. Table A-4 Presentation of LUNs in Active-Passive Mode Controller Status Controller 1 Host Port 0 (FC1) Both Controller 1 controllers LUNs online Controller 1 Inactive failed Controller 2 Controller 1 failed LUNs Controller 1 Host Port 1 (FC2) Inactive Inactive Controller 2 LUNs Controller 2 Host Port 0 (FC1) Inactive Controller 1 LUNs Inactive Controller 2 Host Port 1 (FC2) Controller 2 LUNs Controller 2 LUNs Inactive 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. A-11