Managing backup data comprises mounting a snapshot of a file system. Each of the plurality of snapshots is taken at a particular time and each comprises a replica of the data set at that particular time. The mounted snapshot is accessed. For each of the one or more file system objects included in the accessed snapshot, index data is added which indicates that each of the one or more file system objects is located within the accessed snapshot. This information is added to an index associated with the snapshot so that it is able to be determined, using the index and without having to again mount the accessed snapshot, whether an object of interest is included in the snapshot.