Adaptec 412R User Guide - Page 119

Theory of Controller Operation Table A-6 Presentation of LUNs in Active-Active Dual-Port Mode Controller Status Both controllers online Controller 1 fails Controller 2 fails Controller 1 Controller 1 Controller 2 Controller 2 FC 1 Host Port FC 2 Host Port FC 1 Host Port FC 2 Host Port Controller 1 Controller 1 Controller 2 Controller 2 LUNs LUNs LUNs LUNs Inactive Controller 1 LUNs Inactive Controller 2 LUNs Controller 2 LUNs Inactive Controller 1 LUNs Inactive In either mode, arrays can only be accessed by the controller that currently owns them. One controller will have no visibility to the others' arrays. If one controller fails, the surviving controller will take ownership of all arrays. Pool spares and unassigned disks are visible to both controllers. The two controllers communicate via the back-end disk buses. Although many different message types are sent between the two controllers, the majority of the data is write cache data. In the default write-back caching mode, any data that the host writes to one controller is copied to the other controller before a good status is returned to the host. By mirroring the data, if a controller fails, the surviving controller will have a copy of all data that has not been written to the disk. Note: The controllers communicate with each other using SCSI initiator IDs 6 and 7 on each of the disk channels. You should not change these IDs. Each controller will send heartbeat messages to its partner controller. If a controller does not receive a heartbeat message within a set time period, it will kill the other controller assuming that it has malfunctioned. After killing the other controller, it will take ownership of the arrays and will activate its passive host port to assume the defunct controller's identity. A-17