SynergyFS: A Stackable File System Creating Synergies between Heterogeneous Storage Devices

Hybrid storage architecture is one efficient method that can optimize the I/O performance, cost, and power consumption of storage systems. Thanks to the advances in semiconductor and optical storage technology, its application area is being expanded. It tries to store data to the most proper medium by considering I/O locality of the data. Data management between heterogeneous storage media is important, but it was manually done by system users. This paper presents an automatic management technique for a hybrid storage architecture. A novel software layer is defined in the kernel between virtual and physical file systems. The proposed layer is a variant of stackable file systems, but is able to move files between heterogeneous physical file systems. For example, by utilizing the semantic information (e.g., file type and owner process), the proposed system optimizes the I/O performance without any manual control. Also as the proposed system concatenates the storage space of physical file systems, its space overhead is negligible. Specific characteristics of the proposed systems are analyzed through performance evaluation.