Big data analysis and a data storing applications require a huge volume of storage and a high I/O performance. Applications can achieve high levels of performance and cost efficiency by exploiting the high I/O performances of direct attached storages (DAS) such as internal HDDs. With the size of stored data ever increasing, it will be difficult to replace servers since internal HDDs contain huge amounts of data. In response to this issue, we propose FlexDAS, which improves the flexibility of direct attached storage by using a disk area network (DAN) without degrading the I/O performance. We developed a prototype FlexDAS switch and quantitatively evaluated the architecture. Results show that the FlexDAS switch can disconnect and connect the HDD to the server in just 1.16 seconds. The I/O performances of the disks connected via the FlexDAS switch were almost the same as the conventional DAS architecture.