Résumé : Power-efficient operation is a desirable property, particularly for large clusters housed in datacenters. Recent work has advocated turning off entire nodes to achieve power-proportionality, but this leads to problems with availability and fault tolerance because of the resulting limits imposed on the replication strategies used by the distributed file systems (DFS) employed in these environments, with counter-measures adding substantial complexity to DFS designs. To achieve power- efficiency for a cluster without impacting data availability and recovery from failures and maintain simplicity in DFS design, our solution exploits cluster nodes that have the ability to operate in at least two extreme system- level power states, characterized by minimum vs. maximum power consumption and performance. The paper describes a cluster built with power-efficient node prototypes and presents experimental evaluations to demonstrate power-efficiency.