/sys$common/syshlp/helplib.hlb EXCHANGE, COPY, Qualifiers, /BEST_TRY_CONTIGUOUS  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /BEST_TRY_CONTIGUOUS
       /NOBEST_TRY_CONTIGUOUS

    Indicates whether the Files-11 output file is to be allocated
    contiguously on a "best effort" basis; that is, whether EXCHANGE
    will attempt to place the file on consecutive physical disk
    blocks. If insufficient contiguous space is available, the file
    occupies the largest available contiguous space plus additional
    extents as necessary for the rest of the allocation. You can
    apply this qualifier only to a Files-11 output file.

    The /BEST_TRY_CONTIGUOUS qualifier has no effect when you copy
    files to magnetic tape volumes. When you would like a file from a
    magnetic tape to be copied contiguously, use both the /ALLOCATION
    and the /BEST_TRY_CONTIGUOUS qualifiers, because the size of
    the file on magnetic tape cannot be determined until after it
    is copied to the disk. If you do not know the exact size of the
    file, overestimate the size and specify /TRUNCATE (along with
    /ALLOCATION and /BEST_TRY_CONTIGUOUS) to avoid wasted space.

    The default is /NOBEST_TRY_CONTIGUOUS.