Compaq Infortrend manual Active-to-Active Configuration, Active-to-Standby Configuration

The two controllers continuously monitor each other. When a controller detects that the other controller is not responding, the working controller will immediately take over and disable the failed controller. However, it is not predictable which one of the controllers should fail. It is necessary to connect all other interfaces to both controllers so that a surviving controller can readily continue all the services provided for the RAID system.

Active-to-Active Configuration

Users can freely assign any logical configuration of drives to both or either of the controllers, then map the logical configurations to the host channel IDs/LUNs. I/O requests from host computer will then be directed to the Primary or the Secondary controller accordingly. The total drive capacity can be divided and equally serviced by both controllers.

The active-to-active configuration engages all system resources to performance. Users may also assign all logical configurations to one controller and let the other act as a standby.

Active-to-Standby Configuration

By assigning all the logical configurations of drives to one controller, the other controller will stay idle and becomes active only when its counterpart fails.

Cache Synchronization

The Write-back caching significantly enhances controller performance. However, if one controller fails in the redundant controller configuration, data cached in its memory will be lost and data inconsistency might occur when the existing controller attempts to complete the writes.

Data inconsistency can be avoided using one or several of the I/O channels as the communications path between the controllers. The cached data is always synchronized in each other's memory. Each controller saves an exact replica of the cache content on its counterpart. In the event of controller or power failure, the unfinished writes will be completed by the existing controller.

Battery Support

Unfinished writes will be cached in memory in write-back mode. If power to the system is discontinued, data stored in the cache memory will be lost. Battery modules can support cache memory for a period of several days allowing the controller to keep the cached data. When two controllers are

Redundant Controller 10-17