VMS Help Sys Parameters, SHADOW_MBR_TMO  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    SHADOW_MBR_TMO controls the amount of time the system tries to
    fail over physical members of a shadow set before removing them
    from the set. The SHADOW_MBR_TMO parameter replaces the temporary
    VMSD3 parameter used in prior releases.

    The SHADOW_MBR_TMO parameter is valid for use only with Phase II
    of Volume Shadowing for OpenVMS. You cannot set this parameter
    for use with Phase I, which is obsolete.

    Use the SHADOW_MBR_TMO parameter (a word) to specify the number
    of seconds, in decimal from 1 to 65,535, during which recovery
    of a repairable shadow set is attempted. If you do not specify
    a value or if you specify 0, the default delay of 120 seconds is
    used.

    Because SHADOW_MBR_TMO is a dynamic parameter, you should use the
    SYSGEN command WRITE CURRENT to permanently change its value.

    SHADOW_MBR_TWO is a DYNAMIC parameter.