Cassandra nodetool repair best practices

The nodetool repair command can be run on either a specified node or on all nodes if a node is not specified. The node that initiates the repair becomes the coordinator node for the operation.

If node it not specified it runs on all the nodes that is responsible for that partition range.

run nodetool repair -pr on every node in the cluster to repair all data. Otherwise, some ranges of data will not be repaired

The nodetool repair -pr option is good for repairs across multiple datacenters.

Note: For Cassandra 2.2 and later, a recommended option for repairs across datacenters: use the -dcpar or --dc-parallel to repair datacenters in parallel.

Nodetool Repair