Since security is of critical importance for modern storage systems, it is imperative to protect stored data from being tampered or disclosed. Although an increasing number of secure storage systems have been developed, there is no way to dynamically choose security services to meet disk requests' flexible security requirements. Furthermore, existing security techniques for disk systems are not suitable to guarantee desired response times of disk requests. We remedy this situation by proposing an adaptive scheme (referred to as AdSeD) that can judiciously select the most appropriate security service for each write request while endeavouring to guarantee the desired response times of all disk requests. Experimental results show that AdSeD significantly improves security and overall performance over an existing scheme by up an average of 199.5% and 213.4%).