Apparatus for preventing malfunction at time of duplex unit failure

An apparatus for preventing malfunction when a failure occurs in a system including a host, a duplex unit having first and second devices which operate as an acting device and a standby device, and a simplex unit controlled by the acting device of the duplex unit, the host in normal operation instructing the first and second devices of the duplex unit to perform an acting/standby changeover, the first and second devices of the duplex unit notifying the simplex unit of whether they are acting or standing by, and the simplex unit accepting control data from the acting device and performing predetermined control, wherein said apparatus includes, in each of said first and second devices:

• a monitoring unit for monitoring failure in its own device;
• means for notifying the other device of a failure in its own device;
• and
• active/standby notification means for notifying the simplex unit of the fact that its own device is acting or standing by when the device becomes the acting device or standby device in response to a command from the host, for notifying the simplex unit of the fact that its own device is now an apparent acting device owing to a failure in the other device when its own device is standing by, and for notifying the simplex unit of the fact that its own device is now an apparent standby device owing to a failure in its own device when its own device is acting.