Our research focuses on autonomic database reorganization for DBMS. Reorganization counteracts structural deterioration in tablespaces to recover performance. Structural deterioration through data updates is inevitable, therefore reorganization is an essential task in database administration. At present, there are only vague metrics of disorganization for judging whether administrator should perform reorganization or not. In this paper, we consider IO behavior inside storage and clarify causal relationship between level of structural deterioration and that of performance deterioration. We propose a method to quantitatively detect performance deterioration for reorganization trigger, and evaluate it with empirical test studies.