1. A data-consistent, distributed unified data set device group that stores a distributed unified data set, the distributed unified data set device group comprising: a first data storage component, within a first supervisor local data-storage device, that stores a first portion of the distributed unified data set, the first supervisor local data-storage device receiving WRITE requests directed to the first portion of the distributed unified data set from a host computer via a communications medium; a second data storage component, within a second subordinate local data-storage device, that stores a second portion of the distributed unified data, the second subordinate local data-storage device; and a mirror unified data set that mirrors the distributed unified data set stored on one or more remote data-storage devices.