Although it does require more operator intervention, additional experience has shown that a higher level of availability can be achieved by specifying hot I/O recovery options (CHPK,OPER) for all three classes of devices: DFLT110, DFLT111, and DFLT112. These options will allow the possibility of automatic recovery before the system requests operator involvement.
Operator involvement might require that the message be issued using the Disabled Console Communication Facility (DCCF). This will occur when a DASD device is attached on the channel path that is undergoing Hot I/O recovery. Unless the installation is prepared to deal with messages issued in DCCF mode, IBM® recommends that operator involvement not be requested by the Hot I/O actions.
For non-DASD devices (DFLT110), CHPK,OPER would allow one automated recovery attempt and then request direction from the operator, depending on how critical the device is. If the device is non-critical to the operation of the system, such as a printer, the operator could then reply BOX. If the device is critical, such as a 3705 Communication Controller, and is properly equipped with multiple paths, such as through a type three channel adapter on the 3705, the operator could reply CHPF. Note that the operator should ensure that all critical devices on the same channel path (CHP) have multiple paths before replying CHPF.
You can choose recovery options other than the defaults or the general recommendations, because of considerations unique to the installation. For example, if all DASDs are configured with multiple paths, each through a different CHP, you might consider specifying CHPK,CHPF for both DFLT111 and DFLT112. This will allow one attempt to recover without loss of resources, then an attempt to recover by removing the CHP attached to the failing device or control unit, but without losing a critical device. If the installation contains DASD devices with only one path, the considerations are the same as for non-DASD.