1. A method of performing an auxiliary copy operation from a backup storage system to a secondary storage system, the method comprising: in response to instructions to copy at least some of a plurality of backed up data blocks from a backup storage system comprising at least one memory device to a secondary storage system, for each of the at least some data blocks: reading, with one or more processors, a previously stored signature value corresponding to the respective data block for sending from the backup storage system to the secondary storage system; and based on an indication as to whether the data block is already stored on the secondary storage system, reading the data block from the at least one memory device for sending to the secondary storage system if the data block exists on the secondary storage system, wherein the signature value and not the data block is read from the at least one memory device if the data block exists on the secondary storage system.