Well, one of the prime reasons for using Cassandra as a data store is its fault-tolerant capabilities. It's not driven by a typical master-slave architecture, where failure of the master becomes a single point of system breakdown. Instead, it harbors a concept of operating in a ring mode so that there is no single point of failure. Whenever required, we can restart the nodes without the dread of bringing the whole cluster down; there are various situations where this capability comes in handy.

There are situations where we need to restart Cassandra, but Cassandra's ring architecture equips the administrator to do this seamlessly with zero downtime for the cluster. This means that in situations such as the following that requires a Cassandra cluster to be restarted, a Cassandra administrator can restart the nodes one by one instead of bringing down the entire cluster and then starting it: