A Highly Recoverable Filesystem for Solid State Drives




Alhussein, Mohammed

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Recovering deleted information from storage drives is a long-standing problem. Prior research has approached information recovery by developing file-carving techniques. However, two issues present significant challenges to on-going efforts. 1) Prior knowledge of file types is required to construct file carvers, including file headers and footers, and 2) fragmentation prevents file carvers from achieving successful recovery. More recently, solid state drives or “SSDs” have become more popular. SSDs provide several advantages over traditional mechanical hard drives. They have smaller sizes, are constructed without moving parts, and provide better performance. However, due to problems such as wear leveling and write amplification in SSDs, files are severely fragmented and thus exacerbate the data recovery problem. In addition, SSDs use TRIM and garbage collection schemes to enhance their performance, which can permanently delete data immediately after a delete operation. In this dissertation, I developed a framework for recovering deleted files without knowing the file types and despite significant fragmentation. I developed the Recovery Filesystem by modifying an existing implementation of the exFat filesystem running on top of FUSE. The central idea underlying the Recovery Filesystem is a special identifier embedded in each data block. The identifier monitors each block by mapping the data block to a single file regardless of the file status, existing or deleted. The block sequence number and creation timestamp are also maintained to facilitate the recovery process. In addition, I developed a garbage collection scheme for SSDs that maximizes data retention without sacrificing SSD performance. The experiments conducted in this dissertation demonstrate that the Recovery Filesystem yields acceptable read/write performance results. In addition, file recovery experiments used to compare the Recovery Filesystem with open source recovery techniques demonstrate that the Recovery Filesystem provides significant advantages in the case of fragmented data.



Data Recovery, Solid State Drives