1. A computer-implemented method for providing cost-effective and durable archival data storage service, comprising: under the control of one or more computer systems of an archival data storage system that are configured with executable instructions, receiving, over a communications network from a requesting computer system, an electronic retrieval request to retrieve a data object from persistent storage, the electronic retrieval request encoding an identifier of the data object; in response to receipt of the electronic retrieval request: initiating a retrieval job to obtain the data object from persistent storage; providing, to the requesting computer system, a retrieval job identifier for the retrieval job that is usable to obtain a status of the retrieval job and that, after the retrieval job is completed, is usable to retrieve the data object; receiving, over the communications network, an electronic download request to download at least a portion of the data object, the electronic download request encoding the retrieval job identifier; and in response to receipt of the electronic download request and as a result of the retrieval job having been completed, providing the at least a portion of the data object for download.