BetRFS: A right-optimized write-optimized file system

William Jannen, Jun Yuan, Yang Zhan, Amogh Akshintala, John Esmet, Yizheng Jiao, Ankur Mittal, Prashant Pandey, Phaneendra Reddy, Leif Walsh, Michael Bender, Martin Farach-Colton, Rob Johnson, Bradley C. Kuszmaul, Donald E. Porter

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


    The Be-tree File System, or BetrFS, (pronounced “better eff ess”) is the first in-kernel file system to use a write-optimized index. Write optimized indexes (WOIs) are promising building blocks for storage systems because of their potential to implement both microwrites and large scans efficiently. Previous work on WOI-based file systems has shown promise but has also been hampered by several open problems, which this paper addresses. For example, FUSE issues many queries into the file system, superimposing read-intensive workloads on top of write-intensive ones, thereby reducing the effectiveness of WOIs. Moving to an in-kernel implementation can address this problem by providing finer control of reads. This paper also contributes several implementation techniques to leverage kernel infrastructure without throttling write performance. Our results show that BetrFS provides good performance for both arbitrary microdata operations, which include creating small files, updating metadata, and small writes into large or small files, and for large sequential I/O. On one microdata benchmark, BetrFS provides more than 4× the performance of ext4 or XFS. BetrFS is an ongoing prototype effort, and requires additional data-structure tuning to match current general-purpose file systems on some operations such as deletes, directory renames, and large sequential writes. Nonetheless, many applications realize significant performance improvements. For instance, an in-place rsync of the Linux kernel source realizes roughly 1.6–22× speedup over other commodity file systems.

    Original languageEnglish (US)
    Title of host publicationProceedings of the 13th USENIX Conference on File and Storage Technologies, FAST 2015
    PublisherUSENIX Association
    Number of pages15
    ISBN (Electronic)9781931971201
    StatePublished - 2015
    Event13th USENIX Conference on File and Storage Technologies, FAST 2015 - Santa Clara, United States
    Duration: Feb 16 2015Feb 19 2015

    Publication series

    NameProceedings of the 13th USENIX Conference on File and Storage Technologies, FAST 2015


    Conference13th USENIX Conference on File and Storage Technologies, FAST 2015
    Country/TerritoryUnited States
    CitySanta Clara

    ASJC Scopus subject areas

    • Hardware and Architecture
    • Computer Networks and Communications
    • Software


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