In some cluster database configurations, some nodes of the cluster have faster access to certain data files than to other data files. RMAN automatically detects this situation, which is known as node affinity awareness. When deciding which channel to use to back up a particular data file, RMAN gives preference to the nodes with faster access to the data files that you want to back up. For example, if you have a three-node cluster, and if node1 has faster read/write access to data files 7, 8, and 9 than the other nodes, then node1 has greater node affinity to those files than node2 and node3.