Infortrend RAID Controller Manual

For every channel that is actively serving I/Os, there is another on
the alternate controller that stays idle and will inherit the task
should its counterpart fail.
B. Controller Failover and Failback
In an unlikely event of controller failure, the existing controller will
acknowledge the situation and disconnect with the failed controller.
The existing controller will then behave as both controllers and serve
all the host I/O requests. System vendors should be contacted for an
immediate replacement of the failed unit.
Replacing a Failed Unit: The replacement controller should
have the same amount of memory and the same version of
firmware installed. However, it is inevitable a replacement
controller is usually running later version of firmware. To solve
this problem, firmware synchronization is supported since
firmware version 3.21. When the replacement is combined with a
redundant controller system, the existing controller will take over
and both controllers will be running the same version of firmware.
Your system vendor should be able to provide an appropriate
replacement controller.
Auto-Failback: Once the failed controller is removed and a
replacement controller is installed, the existing controller will
acknowledge the situation. The existing controller will
automatically combine with the replacement controller (IFT-
3102U2G and above). When the initialization process is
completed, the replacement controller will perform as the
Secondary controller. Then both controllers will be restored to the
original configuration that was preserved before controller failure.
If the existing controller fails to re-establish this connection, you
can also choose to "de-assert" the replacement controller through
the existing controller so that both will serve the original system
drive mapping.
C. Active-to-Active Configuration:
Active-to-active configuration conducts all system resources to
performance. Logical units (a logical drive, logical volume, or one of
its logical partitions) can be mapped to either the Primary ID or the
Secondary ID on host channel. This allows a flexible assignment of
different logical units to different controllers. Each controller serves
the logical unit(s) mapped to its host ID/LUN during normal
operation. Workload can then be manually distributed between
controllers.
D. Traffic Distribution and Failover Process
The diagram below illustrates a four-channel configuration using
channel 0 as the communications path. Channel 1 serves as the host
Redundant Controller 12-7