1. A method for rebuilding at least a portion of a signature database that reflects contents of an archive copy of a data set, comprising: receiving a substantially unique identifier for data objects within the data set; storing the substantially unique identifiers in a signature database, wherein a substantially unique identifier for a data object reflects contents of the data object; storing the data set as an archive copy having one or more data chunks, wherein each chunk is stored with header information that includes at least one substantially unique identifier; receiving an indication that the signature database is unrecoverable or unavailable; determining at least one substantially unique identifier within the header information; and using the determined at least one substantially unique identifier from the header information in order to rebuild at least part of the signature database.