SHADOWING loads the host-based volume shadowing driver. See VSI
    Volume Shadowing for OpenVMS for more information about setting
    system parameters for volume shadowing.

    Specify one of the following values:

    Value  Description

    0      No shadowing is enabled; SHDRIVER is not loaded. This is
           the default value.

    2      Host-based volume shadowing enabled; SHDRIVER is loaded.
           Host-based volume shadowing provides shadowing of all
           disks located on a standalone system or an OpenVMS Cluster
           system.