MIFS: A low overhead and efficient mixture file index management method in flash file system

Abstract

Emerging resource-scarce embedded systems, such as Leo satellites, face significant challenges in file system design due to the highly asymmetric sizes of main memory and storage devices. Adopting an in-storage file system to manage raw flash memory can effectively minimize data transfer latency. Existing works focus on reducing the memory footprints of file management but ignore the performance of file accesses. In this paper, we propose a new design of file index taking advantage of the continuity of data pages in the flash memory. The proposed file index manages a series of contiguous physical spaces with a $B^{+}$ tree, which ensures a deterministic time to locate the file data with small memory footprints. Furthermore, we propose a two-mode page allocation mechanism to improve the performance of write operations. Based on these designs, we implement a file system called MIFS in a real embedded system. Experimental results show that MIFS can reduce 36.1% of memory footprint than YAFFS2, the typical embedded flash file system with a similar file access performance. Furthermore, MIFS can achieve 2.23$\times$, 1.35$\times$, 214$\times$, and 84% performance improvement over ELOFS, the state-of-the-art file system for resource-scarce embedded systems, for write, read, update, and file system unmount operations, respectively.