File system fragmentation: Difference between revisions

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Revision as of 07:15, 2 November 2020

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==Negative consequences==

File system fragmentation is more problematic with consumer-grade [[hard disk drive]]s because of the increasing disparity between [[sequential access]] speed and [[rotational latency]] (and to a lesser extent [[seek time]]) on which file systems are usually placed.<ref name="seagate-future">{{cite conference |first=Mark H. |last=Kryder |publisher=[[Seagate Technology]] |date=2006-04-03 |title=Future Storage Technologies: A Look Beyond the Horizon |conference=Storage Networking World conference |url=http://www.snwusa.com/documents/presentations-s06/MarkKryder.pdf |archiveurl=https://web.archive.org/web/20060717001830/http://www.snwusa.com/documents/presentations-s06/MarkKryder.pdf |archivedate=17 July 2006}}</ref> Thus, fragmentation is an important problem in file system research and design. The containment of fragmentation not only depends on the on-disk format of the file system, but also heavily on its implementation.<ref name="mcvoy-extent">{{cite conference |first=L. W. |last=McVoy |first2=S. R. |last2=Kleiman |date=Winter 1991 |title=Extent-like Performance from a UNIX File System |booktitle=Proceedings of [[USENIX]] winter '91 |pages=33–43 |___location=Dallas, Texas |publisher=[[Sun Microsystems, Inc.]] |url=http://www.cis.upenn.edu/~bcpierce/courses/dd/papers/mcvoy-extent.ps |format=[[PostScript]] |accessdate=2006-12-14 }}</ref> File system fragmentation has less performance impact upon [[solid-state drive]]s, as there is no mechanical [[seek time]] involved.<ref name=":0">{{Cite web|url = http://www.hanselman.com/blog/TheRealAndCompleteStoryDoesWindowsDefragmentYourSSD.aspx|title = The real and complete story - Does Windows defragment your SSD?|date = 3 December 2014|accessdate = |website = Scott Hanselman's blog |last = Hanselman|first = Scott}}</ref> However, the file system needs to store one additional piece of metadata for theeach correspondingnon-contiguous part of the file. Each piece of metadata itself occupies space and requires processing power and processor time. If the maximum fragmentation limit is reached, write requests fail.<ref name=":0" />

In simple file system [[benchmark (computing)|benchmark]]s, the fragmentation factor is often omitted, as realistic aging and fragmentation is difficult to model. Rather, for simplicity of comparison, file system benchmarks are often run on empty file systems. Thus, the results may vary heavily from real-life access patterns.<ref name="workload-benchmarks">{{cite journal |first=Keith Arnold |last=Smith |date=January 2001 |title=Workload-Specific File System Benchmarks |publisher=[[Harvard University]] |___location=[[Cambridge, Massachusetts]] |url=http://www.eecs.harvard.edu/vino/fs-perf/papers/keith_a_smith_thesis.pdf |accessdate=2006-12-14 |url-status=dead |archiveurl=https://web.archive.org/web/20041117233607/http://www.eecs.harvard.edu/vino/fs-perf/papers/keith_a_smith_thesis.pdf |archivedate=2004-11-17 }}</ref>