A first computer system calculates a first value as a function of a data block. A second computer system compares the calculated first value with each of a plurality of values in a plurality of entries, respectively. The plurality of entries include a plurality of storage location pointers, respectively, that correspond to a plurality of data blocks, respectively, that were transmitted to a storage system before the first computer system calculated the first value. If the first value compares equally to a value contained in one of the plurality of entries, a storage location pointer of the one entry is transmitted to the storage system, wherein the storage location pointer corresponds to a copy of the data block that was sent to the storage system before the first computer system calculated the first value. If the calculated first value does not compare equally with any value contained in the plurality of entries, the first computer system transmits the data block to the storage system.