1. A method of managing backup data, comprising: accessing a snapshot of a data set, wherein the data set includes at least one object and there is a plurality of snapshots of the data set, each of the plurality of snapshots being taken at a particular time and each comprising a replica of the data set at that particular time; and adding to an index stored in storage and associated with at least the accessed snapshot, with respect to each of one or more objects included in the accessed snapshot, index data indicating at least where each of the one or more objects is located within the accessed snapshot so that it is able to be determined using the index and without again accessing the accessed snapshot whether an object of interest is included in the accessed snapshot and if so, where the object of interest is located within the accessed snapshot, wherein the index is configured to be used to determine, without having to mount the accessed snapshot, whether the object of interest is included in the accessed snapshot.