VMS Help CREATE, /DIRECTORY, Qualifiers, /ALLOCATION  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /ALLOCATION=n

    This qualifier applies only to Files-11 ODS-2 volumes. It
    specifies the initial number of blocks to be allocated to each
    of the specified directories. The default allocation is 1 block.

    This qualifier is useful for creating large directories, for
    example MAIL.DIR;1. It can improve performance by avoiding the
    need for later dynamic expansion of the directory.