How dose zookeeper handle fault-detect in distributed storage system

[fengguang gong]

Hi all:
        
        Recently my lab want to use zk to manager our cluster(Fault detect). 
Our cluster 
includes three kinds of node:
1. dispatch node : load balance and dispatch data.
2. store node: receive data from dispatch node and store.
3. middleware: query data from all the store node.
Here my question is : How dose zk handle fault-detect in this system(how dose 
dispatch node 
and middleware know that a store node is down).