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

    MVTIMEOUT is the time in seconds that a mount verification
    attempt continues on a given disk volume. If the mount
    verification does not recover the volume within that time, the
    I/O operations outstanding to the volume terminate abnormally.

    MVTIMEOUT is a DYNAMIC parameter. On Alpha systems, MVTIMEOUT is
    also an AUTOGEN parameter.