Improving file system performance of mobile storage systems using a decoupled defragmenter

Sangwook Shane Hahn*, Sungjin Lee, Cheng Ji, Li-Pin Chang, Inhyuk Yee, Liang Shi, Chun Jason Xue, Jihong Kim

*Corresponding author for this work

Research output: Chapter in Book/Report/Conference proceedingConference contribution

12 Scopus citations

Abstract

In this paper, we comprehensively investigate the file fragmentation problem on mobile flash storage. From our evaluation study with real Android smartphones, we observed two interesting points on file fragmentation on flash storage. First, defragmentation on mobile flash storage is essential for high I/O performance on Android smartphones because file fragmentation, which is a recurring problem (even after defragmentation), can significantly degrade I/O performance. Second, file fragmentation affects flash storage quite differently than HDDs. When files are fragmented on flash storage, the logical fragmentation and the physical fragmentation are decoupled and a performance degradation mostly comes from logical fragmentation. Motivated by our observations, we propose a novel defragger, janus defragger (janusd), which supports two defraggers, janusdL for a logical defragger and janusdP for a physical defragger. JanusdL, which takes advantage of flash storage's internal logical to physical mapping table, supports logical defragmentation without data copies. JanusdL is very effective for most fragmented files while not sacrificing the flash lifetime. JanusdP, which is useful for physically fragmented files but requires data copies, is invoked only when absolutely necessary. By adaptively selecting janusdL and janusdP, janusd achieves the effect of full file defragmentation without reducing the flash lifetime. Our experimental results show that janusd can achieve at least the same level of I/O performance improvement as e4defrag without affecting the flash lifetime, thus making janusd an attractive defragmentation solution for mobile flash storage.

Original languageEnglish
Title of host publicationProceedings of the 2017 USENIX Annual Technical Conference, USENIX ATC 2017
PublisherUSENIX Association
Pages759-771
Number of pages13
ISBN (Electronic)9781931971386
StatePublished - 1 Jan 2019
Event2017 USENIX Annual Technical Conference, USENIX ATC 2017 - Santa Clara, United States
Duration: 12 Jul 201714 Jul 2017

Publication series

NameProceedings of the 2017 USENIX Annual Technical Conference, USENIX ATC 2017

Conference

Conference2017 USENIX Annual Technical Conference, USENIX ATC 2017
CountryUnited States
CitySanta Clara
Period12/07/1714/07/17

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  • Cite this

    Hahn, S. S., Lee, S., Ji, C., Chang, L-P., Yee, I., Shi, L., Xue, C. J., & Kim, J. (2019). Improving file system performance of mobile storage systems using a decoupled defragmenter. In Proceedings of the 2017 USENIX Annual Technical Conference, USENIX ATC 2017 (pp. 759-771). (Proceedings of the 2017 USENIX Annual Technical Conference, USENIX ATC 2017). USENIX Association.