1. A method performed by a computer system for storing data objects to sequential media, wherein the computer system includes a processor and memory, the method comprising: receiving a set of data objects from multiple computing systems, wherein the set of data objects includes at least two similar data objects; for at least some of the data objects in the set determining if a copy of a data object is already stored on random-access media, wherein the determining includes accessing an index that contains, for data objects already stored on the random-access media an identifier of the data object; and a location of the data object on the random-access media, wherein the index is stored on the random-access media; if the data object is already stored on the random-access media, then identifying a location of the data object on the random-access media and storing on the random-access media a reference to the identified location; if the data object is not already stored on the random-access media, then storing the data object on the random-access media; receiving a request to copy the data objects and the references stored on the random-access media to sequential media; and copying to the sequential media, by the computer system, the data objects and reference data related to the references from the random-access media, wherein the reference data on the sequential media refer to locations of the data objects on the sequential media.