Adaptec 412R User Guide - Page 110

DuraStor 412R/6320SS/7320SS Installation and User's Guide 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. Warning: The controllers communicate with each other using SCSI Initiator IDs 6 and 7 on each of the disk channels. You should not change these ID settings. Each controller sends 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-8