Interestingly, even though HBase uses Zookeeper for coordination, it does not use it for fencing. Instead, fencing is handled by atomic "log-rolling" operations on the HDFS namenode, which can be configured to use its own quorum-based journal. (The equivalent of a "token" is the monotonically-increasing namenode operation sequence number.) So the principle is the same: the system responsible for doing mutual exclusion, and the system that actually stores the data, must be coupled.