VMS Help DECnet-Plus, DCL Commands, APPEND, Qualifiers, /ALLOCATION  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /ALLOCATION
       /ALLOCATION=n

    Qualifier type:      Output file qualifier

    Supported file       Local and remote
    types:

    This qualifier sets the initial allocation for the output file to
    the number of 512-byte blocks specified by n.

    Default value:         Size of input file