Filesystem Aging: It’s more Usage than Fullness

Authors: 

Alex Conway and Eric Knorr, Rutgers University; Yizheng Jiao, The University of North Carolina at Chapel Hill; Michael A. Bender, Stony Brook University; William Jannen, Williams College; Rob Johnson, VMware Research; Donald Porter, The University of North Carolina at Chapel Hill; Martin Farach-Colton, Rutgers University

Abstract: 

Filesystem fragmentation is a first-order performance problem that has been the target of many heuristic and algorithmic approaches. Real-world application benchmarks show that common filesystem operations cause many filesystems to fragment over time, a phenomenon known as filesystem aging.

This paper examines the common assumption that space pressure will exacerbate fragmentation. Our microbenchmarks show that space pressure can cause a substantial amount of inter-file and intra-file fragmentation. However, on a “real-world” application benchmark, space pressure causes fragmentation that slows subsequent reads by only 20% on ext4, relative to the amount of fragmentation that would occur on a file system with abundant space. The other file systems show negligible additional degradation under space pressure.

Our results suggest that the effect of free-space fragmentation on read performance is best described as accelerating the filesystem aging process. The effect on write performance is non-existent in some cases, and, in most cases, an order of magnitude smaller than the read degradation from fragmentation cause by normal usage.

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BibTeX
@inproceedings {234739,
author = {Alex Conway and Eric Knorr and Yizheng Jiao and Michael A. Bender and William Jannen and Rob Johnson and Donald Porter and Martin Farach-Colton},
title = {Filesystem Aging: It{\textquoteright}s more Usage than Fullness},
booktitle = {11th {USENIX} Workshop on Hot Topics in Storage and File Systems (HotStorage 19)},
year = {2019},
address = {Renton, WA},
url = {https://www.usenix.org/conference/hotstorage19/presentation/conway},
publisher = {{USENIX} Association},
month = jul,
}