IBM Midrange System DS4000 Series Hardware Manual page 59

The interconnect module is the unit (FRU) between the two controller support modules. The
interconnect holds the cache batteries and the new hot-swappable midplane. When the
interconnect module is removed, the DS5000 storage subsystem automatically suspends
controller B, fails over all the LUNs to controller A, and continues to operate. The midplane
has batteries, so write caching is disabled for the default settings of the LUNs. If you still want
to use cache for writing, open Storage Manager, select a volume, and select Logical Drive 
Change  Cache settings  Enable write caching without batteries. You can find more
details about this topic in Chapter 4, "IBM System Storage DS planning and configuration" on
page 103.
Possible loss of data: When you use the feature Enable write caching without batteries,
you can lose data in a cache when the batteries are removed or discharged and power
fails.
When the interconnect module is put back in place, the DS5000 storage subsystem can
revert back to normal operation. If the operating system uses non-AVT path failover drivers,
you have to manually redistribute the LUNs to their respective owning controller (A or B). All
the components depicted in Figure 3-14 are hot-swappable and can be replaced on-the-fly to
ensure that users do not incur any downtime.
Figure 3-14 Front view of the DS5000 storage subsystem
Interconnect Module
Controller Support Modules
Chapter 3. IBM System Storage DS4000 and DS5000 hardware
41