Kernel Korner - Unionfs: Bringing Filesystems Together
Unionfs recursively merges several underlying directories or branches into a single virtual view. The efficient fan-out structure of Unionfs makes it suitable for many applications. Unionfs can be used to provide merged distribution ISOs, a single /home namespace and more. Unionfs's copy-on-write semantics make it useful for source code versioning, snapshotting and patching CD-ROMs. We benchmarked Unionfs's performance under Linux 2.4. For a compile benchmark with one to four branches, Unionfs overhead is only 12%. For an I/O intensive workload, the overhead ranges from 10% for a single branch to 12% for four branches.
Thanks to Puja Gupta, Harikesavan Krishnan, Mohammad Zubair and Jay Dave, who also were on the Unionfs development team. Special thanks go to Mohammad for helping to get the software for this article prepared for release.
Resources for this article: www.linuxjournal.com/article/7812.
Charles P. Wright (firstname.lastname@example.org) is a Computer Science PhD student at Stony Brook University. Charles conducts operating systems research with a focus on filesystems, security and extensibility. He also is active in the Linux Users Group at Stony Brook (LUGSB).
Erez Zadok (email@example.com) is on the Computer Science faculty at Stony Brook University, the author of Linux NFS and Automounter Administration (Sybex, 2001), the creator and maintainer of the FiST stackable templates system and the primary maintainer of the Am-utils (aka Amd) automounter. Erez conducts operating systems research with a focus on filesystems, security, versatility and portability.
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