1. A storage system storing a plurality of content data, and a plurality of original metadata and back-up metadata associated with the plurality of content data, the storage system comprising: a first node including a first processor; and a plurality of second nodes, each having a first storage region storing one or more original metadata of the plurality of original metadata and a second storage region storing one or more back-up metadata of the plurality of back-up metadata, and each including a second processor being configured to manage the first storage region and the second storage region; wherein on receipt of a first query, requesting a list of content data and/or metadata that satisfies a given criterion, by the first node, the first processor is configured to issue a second query, requesting a list of content data and/or metadata that satisfies the given criterion, to each of the plurality of second nodes, wherein on receipt of the second query by each of the plurality of second nodes, the second processor of each of the plurality of second nodes is configured to search only its own first storage region out of its own first and second storage regions, for content data and/or metadata related to the given criterion, and provide result of the second query to the first node, and wherein the first processor in the first node is further configured to aggregate the result sent from each of the plurality of second nodes.