A system and method are described to improve the efficiency of copy-on-write operations in a storage system. A PDSS descriptor associated with partition PSS and a PDTT descriptor associated with partition PTT are maintained in a cache memory, with partition PSS associated with a source logical unit LU.sub.S and partition PTT associated with a source logical unit LU.sub.T. An ICP flag is set in the PDSS and PDTT descriptors indicating that the PSS and PTT are undergoing a copy-on-write operation. Data is then dissociated with PTT and locations of each block of the PSS stored in memory are copied from the PDSS descriptor to the PDTT descriptor. A task is then created to fetch blocks of the PSS and the fetched blocks are copied from the PSS to the PTT.