VMS Help BACKUP Command, Qualifiers, /GROUP_SIZE  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /GROUP_SIZE=n

    Output Save-Set Qualifier

    Defines the number of blocks BACKUP places in each redundancy
    group. The value of n must be 0 to 100.

    If you define a value of 0 for /GROUP_SIZE, no redundancy groups
    are created for the save set. /GROUP_SIZE=10 is the default
    value.