PURPOSE: To easily analyze the contents of a fault by sampling trace data at the time of fault generation to a memory in the internal part of a communication control processing system by a host connecting mechanism.

CONSTITUTION: When a designated request is completed to an input/output designation code to input/output control 24 of a host connecting mechanism 21, a fault detecting means 27 in a host connecting mechanism control driver 22 analyzes the contents of an operation end state in an input/output request block. In the case of a normal end, the next input/output request is executed and in the case of an abnormal end, notification is executed to a trace sampling means 28. According to the notification from the fault detecting means 27, the contents of a memory 26 for local trace in the internal part of the host connecting mechanism 21 are sampled to a memory 29 for trace sample by a trace sampling means 28.