1. A file server comprising: a data storage, the data storage comprising one or more data storage devices and a plurality of slices of the data storage; a processor coupled to the data storage for accessing data stored on the one or more data storage devices; and a unified file system component comprising a unified slice map volume, wherein the file server has a file server architecture including a file system layer and a passive sparse volume layer, the file system layer having associated file system metadata describing a state of the unified file system and a set of file system functions, and the passive sparse volume layer having associated sparse volume metadata describing a set of sparse volume functions and a state of one or more volumes in the passive sparse volume layer, wherein the unified slice map volume is operative to store the sparse volume metadata, the file system metadata, and slice allocation metadata comprising a slice allocation status of each slice in the plurality of slices, and wherein the unified file system is operative: to perform a unified set of functions that include the file system functions and the sparse volume functions, the sparse volume functions being associated with one or more of creating, caching, maintaining, and updating the sparse volume metadata associated with the passive sparse volume layer; and to update a slice allocation status entry for a selected slice in the plurality of slices in response to performance of a slice allocation process allocating the selected slice to a logical unit of the data storage.