A network storage appliance integrates a plurality of servers and a
plurality of storage controllers into a single chassis. The storage
controllers control transfers of data between the servers and storage
devices controlled by the storage controllers. The servers and storage
controllers comprise a plurality of field replaceable units (FRUs) that
plug into a backplane also enclosed in the chassis. The FRUs are
redundant such that any one of the FRUs may fail without incurring loss
of availability of the data stored on the storage devices. One of the
storage controllers detects a failure of one of the servers and
responsively kills the failed server. The failure may be a stopped
heartbeat from the failed server. Additionally, one of the storage
controllers detects a failure of a heartbeat link coupling the servers
and responsively inactivates one of the servers to enable failover to the
live server.