The SET SHADOW command and its qualifiers are designed to give
    the user greater control over the behavior of shadow sets. These
    commands act upon the shadow set (also known as the virtual unit)
    or, in some cases, on the individual shadow set member that you
    specify.

    Unless otherwise noted, the qualifier settings typically remain
    in effect until they are changed using either the SET SHADOW
    or SET DEVICE command or until the shadow set or shadow set
    member is dismounted. If the shadow set is remounted or a shadow
    set member is returned to the shadow set from which it was
    dismounted, the settings must be specified again.

    Some SET SHADOW qualifiers also can be specified using the SET
    DEVICE command, where they have the same effect. However, if
    your focus is on changing characteristics of shadow sets, the SET
    SHADOW command provides more options.