A method and apparatus for selectively storing data on a server. The method operates by accessing a computer file and defining a data block as a current block of data. The current block is subsequently checksummed using a rolling error identification code. The method then determines if the calculated checksum for the current block has been previously stored in a database. If a matching checksum for the data is found in the database, then a duplicate of the current block already exists and the process repeats by selecting a new block of data. Alternatively, if the calculated checksum is absent from the checksum and the process has advanced one block length, the process moves back one block length and stores the current block in an archive. Otherwise, the checksum advances one byte forward to form a new current block of data and the process repeats.