# Failure to Update the Schema

ScyllaDB relies on the Raft consensus algorithm, which requires at least a quorum
of nodes in a cluster to be available. If some nodes are down and the quorum is
lost, schema updates fail.

See [Handling Node Failures](https://docs.scylladb.com/manual/master/troubleshooting/handling-node-failures.md) for information about
recovery actions depending on the number of nodes and DCs in your cluster.