Infortrend RAID Controller Manual

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 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 grouped into several logical configurations
and equally assigned to both controllers allowing both to share the
workload.
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
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 two of the I/O
channels as the communications path between the controllers. The
controllers communicating over the path are constantly
synchronizing the cached data 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.
For the IFT-3102 or 3101 series, RS-232C cable can be used for
redundant controller configuration, but the connection does not
support the heavy traffic load for synchronizing cached data. It is
recommended to apply write-through caching instead.
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 operating in write-back mode, it is
recommended to install a battery module to each controller.
Redundant Controller 12-15