12. A network storage server node comprising: a network module using which the node can communicate with a network storage client; a data module using which the node can manage a persistent storage subsystem; and a management host configured to provide management services of the network storage server node and to interface with an external administrative user, the management host including a metadata subsystem to store and retrieve metadata of a plurality of types, relating to a plurality of data objects stored in a distributed object store implemented at least partially in the persistent storage subsystem, wherein the metadata subsystem is configured to store the metadata in locations that are independent of locations where corresponding data objects of the plurality of data objects are stored, the plurality of types of metadata including system defined metadata, inferred metadata and user-defined metadata, wherein the inferred metadata includes latent metadata and discovered metadata, wherein latent metadata includes data gathered by an application from the data associated with the plurality of data objects, the gathered data subsequently being stored as metadata relating to the plurality of data objects, wherein discovered metadata includes relational information derived by the application from the data associated with the plurality of data objects, the relational information describing a relationship between two or more data objects of the plurality of data objects, the metadata subsystem further being capable of searching the metadata of the plurality of types to identify data objects that satisfy user-specified search queries, wherein the metadata subsystem is configured to implement a plurality of mutually isolated query domains, wherein said metadata includes a plurality of metadata attribute-value pairs, wherein each of the metadata attribute-value pairs is assigned to one of the plurality of query domains, wherein each query domain of the plurality of mutually isolated query domains is a logical construct used to isolate the metadata attribute-value pairs assigned to the particular query domain from the metadata attribute-value pairs assigned to the other query domains of the plurality of query domains, and wherein each operation performed by the metadata subsystem is performed within the context of at least one of the plurality of query domains.
16. A network storage server node as recited in claim 12 , wherein the metadata subsystem is configured to allow both fixed-schema storage and flexible-schema storage to be used to store metadata associated with the plurality of data objects.