1. A data file storage management system for use in a dynamically mapped virtual data storage subsystem to maintain data file integrity in copy operations, wherein said dynamically mapped virtual data storage subsystem comprises a set of data storage devices for storage of data files, said data file copy management system comprising: a first mapping table which associates a virtual address assigned to a received data file with an immutable identification; a second mapping table which associates said immutable identification to a logical address which identifies a physical storage location on a one of said data storage devices for storage of said received data file; means for storing said received data file as indicated by said logical address; means, responsive to relocation of said stored data file, for updating said second mapping table to reflect relocation of said stored data file exclusive of updating said first mapping table; and means, responsive to a request to copy said received data file to a second virtual address, for updating said first mapping table to associate said second virtual address with said immutable identification.