/sys$common/syshlp/helplib.hlb Sys Parameters, MSCP_SERVE_ALL  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    MSCP_SERVE_ALL is a bit mask that controls disk serving in an
    OpenVMS Cluster. A disk is served regardless of its allocation
    class unless bit 3 has a value of 1.

    Starting with OpenVMS Version 7.2, the serving types are
    implemented as a bit mask. To specify the type of serving your
    system will perform, locate the type you want in the following
    table and specify its value. For some systems, you may want to
    specify two serving types, such as serving the system disk and
    serving locally attached disks. To specify such a combination,
    add the values of each type, and specify the sum.

    In a mixed-version cluster that includes any systems running
    OpenVMS Version 7.1-x or earlier, serving all available disks
    is restricted to serving all disks except those whose allocation
    class does not match the system's node allocation class (pre-
    Version 7.2). To specify this type of serving, use the value 9
    (which sets bit 0 and bit 3).

    The following table describes the serving type controlled by each
    bit and its decimal value.

    Bit and
    Value
    When Set   Description

    Bit 0      Serve all available disks (locally attached and those
    (1)        connected to HSx and DSSI controllers). Disks with
               allocation classes that differ from the system's
               allocation class (set by the ALLOCLASS parameter) are
               also served if bit 3 is not set.

    Bit 1      Serve locally attached (non-HSx and DSSI) disks.
    (2)

    Bit 2      Serve the system disk. This is the default setting.
    (4)        This setting is important when other nodes in the
               cluster rely on this system being able to serve its
               system disk. This setting prevents obscure contention
               problems that can occur when a system attempts to
               complete I/O to a remote system disk whose system has
               failed.

    Bit 3      Restrict the serving specified by bit 0. All disks
    (8)        except those with allocation classes that differ from
               the system's allocation class (set by the ALLOCLASS
               parameter) are served.

               This is pre-Version 7.2 behavior. If your cluster
               includes systems running OpenVMS 7.1-x or earlier,
               and you want to serve all available disks, you must
               specify 9, the result of setting this bit and bit 0.

    Although the serving types are now implemented as a bit mask, the
    values of 0, 1, and 2, specified by bit 0 and bit 1, retain their
    original meanings:

    o  0 - Do not serve any disks (the default for earlier versions
       of OpenVMS).

    o  1 - Serve all available disks.

    o  2 - Serve only locally attached (non-HSx and non-DSSI) disks.

    If the MSCP_LOAD system parameter is 0, MSCP_SERVE_ALL is
    ignored.