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</a> mergerfs </label> <div class="md-nav__source"> <a href="https://github.com/trapexit/mergerfs" title="Go to repository" class="md-source" data-md-component="source"> <div class="md-source__icon md-icon"> <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 448 512"><!--! Font Awesome Free 6.7.2 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2024 Fonticons, Inc.--><path d="M439.55 236.05 244 40.45a28.87 28.87 0 0 0-40.81 0l-40.66 40.63 51.52 51.52c27.06-9.14 52.68 16.77 43.39 43.68l49.66 49.66c34.23-11.8 61.18 31 35.47 56.69-26.49 26.49-70.21-2.87-56-37.34L240.22 199v121.85c25.3 12.54 22.26 41.85 9.08 55a34.34 34.34 0 0 1-48.55 0c-17.57-17.6-11.07-46.91 11.25-56v-123c-20.8-8.51-24.6-30.74-18.64-45L142.57 101 8.45 235.14a28.86 28.86 0 0 0 0 40.81l195.61 195.6a28.86 28.86 0 0 0 40.8 0l194.69-194.69a28.86 28.86 0 0 0 0-40.81"/></svg> </div> <div class="md-source__repository"> mergerfs </div></a> </div> <ul class="md-nav__list" data-md-scrollfix> <li class="md-nav__item"> <a href=".." class="md-nav__link"> <span class="md-ellipsis"> Home </span>
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<li class="md-nav__item"> <a href="../quickstart/" class="md-nav__link"> <span class="md-ellipsis"> QuickStart </span>
</a> </li>
<li class="md-nav__item md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type="checkbox" id="__nav_3" > <label class="md-nav__link" for="__nav_3" id="__nav_3_label" tabindex="0"> <span class="md-ellipsis"> Installation </span>
<span class="md-nav__icon md-icon"></span> </label> <nav class="md-nav" data-md-level="1" aria-labelledby="__nav_3_label" aria-expanded="false"> <label class="md-nav__title" for="__nav_3"> <span class="md-nav__icon md-icon"></span> Installation </label> <ul class="md-nav__list" data-md-scrollfix> <li class="md-nav__item"> <a href="../setup/installation/" class="md-nav__link"> <span class="md-ellipsis"> Installation </span>
</a> </li>
<li class="md-nav__item"> <a href="../setup/upgrade/" class="md-nav__link"> <span class="md-ellipsis"> Upgrade </span>
</a> </li>
<li class="md-nav__item"> <a href="../setup/build/" class="md-nav__link"> <span class="md-ellipsis"> Build </span>
</a> </li>
</ul> </nav> </li>
<li class="md-nav__item"> <a href="../terminology/" class="md-nav__link"> <span class="md-ellipsis"> Terminology </span>
</a> </li>
<li class="md-nav__item md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type="checkbox" id="__nav_5" > <label class="md-nav__link" for="__nav_5" id="__nav_5_label" tabindex="0"> <span class="md-ellipsis"> Config </span>
<span class="md-nav__icon md-icon"></span> </label> <nav class="md-nav" data-md-level="1" aria-labelledby="__nav_5_label" aria-expanded="false"> <label class="md-nav__title" for="__nav_5"> <span class="md-nav__icon md-icon"></span> Config </label> <ul class="md-nav__list" data-md-scrollfix> <li class="md-nav__item"> <a href="../config/options/" class="md-nav__link"> <span class="md-ellipsis"> Options </span>
</a> </li>
<li class="md-nav__item"> <a href="../config/deprecated_options/" class="md-nav__link"> <span class="md-ellipsis"> Deprecated Options </span>
</a> </li>
<li class="md-nav__item"> <a href="../config/branches/" class="md-nav__link"> <span class="md-ellipsis"> branches </span>
</a> </li>
<li class="md-nav__item"> <a href="../config/functions_categories_and_policies/" class="md-nav__link"> <span class="md-ellipsis"> functions, categories and policies </span>
</a> </li>
<li class="md-nav__item"> <a href="../config/func_readdir/" class="md-nav__link"> <span class="md-ellipsis"> func.readdir </span>
</a> </li>
<li class="md-nav__item"> <a href="../config/rename_and_link/" class="md-nav__link"> <span class="md-ellipsis"> rename and link </span>
</a> </li>
<li class="md-nav__item"> <a href="../config/cache/" class="md-nav__link"> <span class="md-ellipsis"> caching </span>
</a> </li>
<li class="md-nav__item"> <a href="../config/readahead/" class="md-nav__link"> <span class="md-ellipsis"> readahead </span>
</a> </li>
<li class="md-nav__item"> <a href="../config/inodecalc/" class="md-nav__link"> <span class="md-ellipsis"> inodecalc </span>
</a> </li>
<li class="md-nav__item"> <a href="../config/threads/" class="md-nav__link"> <span class="md-ellipsis"> threads </span>
</a> </li>
<li class="md-nav__item"> <a href="../config/pin-threads/" class="md-nav__link"> <span class="md-ellipsis"> pin-threads </span>
</a> </li>
<li class="md-nav__item"> <a href="../config/link_cow/" class="md-nav__link"> <span class="md-ellipsis"> link_cow </span>
</a> </li>
<li class="md-nav__item"> <a href="../config/fuse_msg_size/" class="md-nav__link"> <span class="md-ellipsis"> fuse_msg_size </span>
</a> </li>
<li class="md-nav__item"> <a href="../config/follow-symlinks/" class="md-nav__link"> <span class="md-ellipsis"> follow-symlinks </span>
</a> </li>
<li class="md-nav__item"> <a href="../config/link-exdev/" class="md-nav__link"> <span class="md-ellipsis"> link-exdev </span>
</a> </li>
<li class="md-nav__item"> <a href="../config/rename-exdev/" class="md-nav__link"> <span class="md-ellipsis"> rename-exdev </span>
</a> </li>
<li class="md-nav__item"> <a href="../config/symlinkify/" class="md-nav__link"> <span class="md-ellipsis"> symlinkify </span>
</a> </li>
<li class="md-nav__item"> <a href="../config/nullrw/" class="md-nav__link"> <span class="md-ellipsis"> nullrw </span>
</a> </li>
<li class="md-nav__item"> <a href="../config/xattr/" class="md-nav__link"> <span class="md-ellipsis"> xattr </span>
</a> </li>
<li class="md-nav__item"> <a href="../config/nfsopenhack/" class="md-nav__link"> <span class="md-ellipsis"> nfsopenhack </span>
</a> </li>
<li class="md-nav__item"> <a href="../config/statfs/" class="md-nav__link"> <span class="md-ellipsis"> statfs / statvfs </span>
</a> </li>
<li class="md-nav__item"> <a href="../config/flush-on-close/" class="md-nav__link"> <span class="md-ellipsis"> flush-on-close </span>
</a> </li>
<li class="md-nav__item"> <a href="../config/export-support/" class="md-nav__link"> <span class="md-ellipsis"> export-support </span>
</a> </li>
</ul> </nav> </li>
<li class="md-nav__item"> <a href="../error_handling_and_logging/" class="md-nav__link"> <span class="md-ellipsis"> Error Handling and Logging </span>
</a> </li>
<li class="md-nav__item"> <a href="../runtime_interfaces/" class="md-nav__link"> <span class="md-ellipsis"> Runtime Interfaces </span>
</a> </li>
<li class="md-nav__item"> <a href="../remote_filesystems/" class="md-nav__link"> <span class="md-ellipsis"> Remote Filesystems </span>
</a> </li>
<li class="md-nav__item"> <a href="../tips_notes/" class="md-nav__link"> <span class="md-ellipsis"> Tips and Notes </span>
</a> </li>
<li class="md-nav__item"> <a href="../known_issues_bugs/" class="md-nav__link"> <span class="md-ellipsis"> Known Issues and Bugs </span>
</a> </li>
<li class="md-nav__item md-nav__item--active"> <input class="md-nav__toggle md-toggle" type="checkbox" id="__toc"> <label class="md-nav__link md-nav__link--active" for="__toc"> <span class="md-ellipsis"> Project Comparisons </span>
<span class="md-nav__icon md-icon"></span> </label> <a href="./" class="md-nav__link md-nav__link--active"> <span class="md-ellipsis"> Project Comparisons </span>
</a>
<nav class="md-nav md-nav--secondary" aria-label="Table of contents"> <label class="md-nav__title" for="__toc"> <span class="md-nav__icon md-icon"></span> Table of contents </label> <ul class="md-nav__list" data-md-component="toc" data-md-scrollfix> <li class="md-nav__item"> <a href="#mhddfs" class="md-nav__link"> <span class="md-ellipsis"> mhddfs </span> </a> </li> <li class="md-nav__item"> <a href="#aufs" class="md-nav__link"> <span class="md-ellipsis"> aufs </span> </a> </li> <li class="md-nav__item"> <a href="#unionfs" class="md-nav__link"> <span class="md-ellipsis"> unionfs </span> </a> </li> <li class="md-nav__item"> <a href="#unionfs-fuse" class="md-nav__link"> <span class="md-ellipsis"> unionfs-fuse </span> </a> </li> <li class="md-nav__item"> <a href="#overlayfs" class="md-nav__link"> <span class="md-ellipsis"> overlayfs </span> </a> </li> <li class="md-nav__item"> <a href="#raid0-jbod-span-drive-concatenation-striping" class="md-nav__link"> <span class="md-ellipsis"> RAID0, JBOD, SPAN, drive concatenation, striping </span> </a> </li> <li class="md-nav__item"> <a href="#unraid" class="md-nav__link"> <span class="md-ellipsis"> UnRAID </span> </a> </li> <li class="md-nav__item"> <a href="#zfs" class="md-nav__link"> <span class="md-ellipsis"> ZFS </span> </a> </li> <li class="md-nav__item"> <a href="#stablebits-drivepool" class="md-nav__link"> <span class="md-ellipsis"> StableBit's DrivePool </span> </a> </li> <li class="md-nav__item"> <a href="#plan9-binds" class="md-nav__link"> <span class="md-ellipsis"> Plan9 binds </span> </a> </li> </ul> </nav> </li>
<li class="md-nav__item"> <a href="../performance/" class="md-nav__link"> <span class="md-ellipsis"> Tweaking Performance </span>
</a> </li>
<li class="md-nav__item"> <a href="../benchmarking/" class="md-nav__link"> <span class="md-ellipsis"> Benchmarking </span>
</a> </li>
<li class="md-nav__item"> <a href="../tooling/" class="md-nav__link"> <span class="md-ellipsis"> Tooling </span>
</a> </li>
<li class="md-nav__item"> <a href="../usage_patterns/" class="md-nav__link"> <span class="md-ellipsis"> Usage Patterns </span>
</a> </li>
<li class="md-nav__item md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type="checkbox" id="__nav_16" > <label class="md-nav__link" for="__nav_16" id="__nav_16_label" tabindex="0"> <span class="md-ellipsis"> FAQ </span>
<span class="md-nav__icon md-icon"></span> </label> <nav class="md-nav" data-md-level="1" aria-labelledby="__nav_16_label" aria-expanded="false"> <label class="md-nav__title" for="__nav_16"> <span class="md-nav__icon md-icon"></span> FAQ </label> <ul class="md-nav__list" data-md-scrollfix> <li class="md-nav__item"> <a href="../faq/reliability_and_scalability/" class="md-nav__link"> <span class="md-ellipsis"> Reliability and Scalability </span>
</a> </li>
<li class="md-nav__item"> <a href="../faq/usage_and_functionality/" class="md-nav__link"> <span class="md-ellipsis"> Usage and Functionality </span>
</a> </li>
<li class="md-nav__item"> <a href="../faq/configuration_and_policies/" class="md-nav__link"> <span class="md-ellipsis"> Configuration and Policies </span>
</a> </li>
<li class="md-nav__item"> <a href="../faq/compatibility_and_integration/" class="md-nav__link"> <span class="md-ellipsis"> Compatibility and Integration </span>
</a> </li>
<li class="md-nav__item"> <a href="../faq/recommendations_and_warnings/" class="md-nav__link"> <span class="md-ellipsis"> Recommendations and Warnings </span>
</a> </li>
<li class="md-nav__item"> <a href="../faq/technical_behavior_and_limitations/" class="md-nav__link"> <span class="md-ellipsis"> Technical Behavior and Limitations </span>
</a> </li>
<li class="md-nav__item"> <a href="../faq/why_isnt_it_working/" class="md-nav__link"> <span class="md-ellipsis"> "Why isn't it working?" </span>
</a> </li>
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<nav class="md-nav md-nav--secondary" aria-label="Table of contents"> <label class="md-nav__title" for="__toc"> <span class="md-nav__icon md-icon"></span> Table of contents </label> <ul class="md-nav__list" data-md-component="toc" data-md-scrollfix> <li class="md-nav__item"> <a href="#mhddfs" class="md-nav__link"> <span class="md-ellipsis"> mhddfs </span> </a> </li> <li class="md-nav__item"> <a href="#aufs" class="md-nav__link"> <span class="md-ellipsis"> aufs </span> </a> </li> <li class="md-nav__item"> <a href="#unionfs" class="md-nav__link"> <span class="md-ellipsis"> unionfs </span> </a> </li> <li class="md-nav__item"> <a href="#unionfs-fuse" class="md-nav__link"> <span class="md-ellipsis"> unionfs-fuse </span> </a> </li> <li class="md-nav__item"> <a href="#overlayfs" class="md-nav__link"> <span class="md-ellipsis"> overlayfs </span> </a> </li> <li class="md-nav__item"> <a href="#raid0-jbod-span-drive-concatenation-striping" class="md-nav__link"> <span class="md-ellipsis"> RAID0, JBOD, SPAN, drive concatenation, striping </span> </a> </li> <li class="md-nav__item"> <a href="#unraid" class="md-nav__link"> <span class="md-ellipsis"> UnRAID </span> </a> </li> <li class="md-nav__item"> <a href="#zfs" class="md-nav__link"> <span class="md-ellipsis"> ZFS </span> </a> </li> <li class="md-nav__item"> <a href="#stablebits-drivepool" class="md-nav__link"> <span class="md-ellipsis"> StableBit's DrivePool </span> </a> </li> <li class="md-nav__item"> <a href="#plan9-binds" class="md-nav__link"> <span class="md-ellipsis"> Plan9 binds </span> </a> </li> </ul> </nav> </div> </div> </div> <div class="md-content" data-md-component="content"> <article class="md-content__inner md-typeset">
<a href="https://github.com/trapexit/mergerfs/edit/master/mkdocs/docs/project_comparisons.md" title="Edit this page" class="md-content__button md-icon"> <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24"><path d="M10 20H6V4h7v5h5v3.1l2-2V8l-6-6H6c-1.1 0-2 .9-2 2v16c0 1.1.9 2 2 2h4zm10.2-7c.1 0 .3.1.4.2l1.3 1.3c.2.2.2.6 0 .8l-1 1-2.1-2.1 1-1c.1-.1.2-.2.4-.2m0 3.9L14.1 23H12v-2.1l6.1-6.1z"/></svg> </a> <a href="https://github.com/trapexit/mergerfs/raw/master/mkdocs/docs/project_comparisons.md" title="View source of this page" class="md-content__button md-icon"> <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24"><path d="M17 18c.56 0 1 .44 1 1s-.44 1-1 1-1-.44-1-1 .44-1 1-1m0-3c-2.73 0-5.06 1.66-6 4 .94 2.34 3.27 4 6 4s5.06-1.66 6-4c-.94-2.34-3.27-4-6-4m0 6.5a2.5 2.5 0 0 1-2.5-2.5 2.5 2.5 0 0 1 2.5-2.5 2.5 2.5 0 0 1 2.5 2.5 2.5 2.5 0 0 1-2.5 2.5M9.27 20H6V4h7v5h5v4.07c.7.08 1.36.25 2 .49V8l-6-6H6a2 2 0 0 0-2 2v16a2 2 0 0 0 2 2h4.5a8.2 8.2 0 0 1-1.23-2"/></svg> </a>
<h1 id="project-comparisons">Project Comparisons</h1><h2 id="mhddfs">mhddfs</h2><ul><li><a href="https://romanrm.net/mhddfs">https://romanrm.net/mhddfs</a></li></ul><p>mhddfs had not been updated in over a decade and has known stabilityand security issues. mergerfs provides a super set of mhddfs' featuresand offers better performance. In fact, as of 2020, the author ofmhddfs has <a href="https://romanrm.net/mhddfs#update">moved to usingmergerfs.</a></p><p>Below is an example of mhddfs and mergerfs setup to work similarly.</p><p><code>mhddfs -o mlimit=4G,allow_other /mnt/drive1,/mnt/drive2 /mnt/pool</code></p><p><code>mergerfs -o minfreespace=4G,category.create=ff /mnt/drive1:/mnt/drive2 /mnt/pool</code></p><h2 id="aufs">aufs</h2><ul><li><a href="https://aufs.sourceforge.net">https://aufs.sourceforge.net</a></li><li><a href="https://en.wikipedia.org/wiki/Aufs">https://en.wikipedia.org/wiki/Aufs</a></li></ul><p>While aufs still is maintained it failed to be included in themainline kernel and is no longer available in most Linux distrosmaking it harder to get installed for the average user.</p><p>While aufs can often offer better peak performance due to beingprimarily kernel based, mergerfs provides more configurability and isgenerally easier to use. mergerfs however does not offer the overlay /copy-on-write (CoW) features which aufs has.</p><h2 id="unionfs">unionfs</h2><ul><li><a href="https://unionfs.filesystems.org">https://unionfs.filesystems.org</a></li></ul><p>unionfs for Linux is a "stackable unification file system" whichfunctions like many other union filesystems. unionfs has not beenmaintained and was last released for Linux v3.14 back in 2014.</p><p>Documentation is sparse so a comparison of features is not possiblebut given the lack of maintenance and support for modern kernels thereis little reason to consider it as a solution.</p><h2 id="unionfs-fuse">unionfs-fuse</h2><ul><li><a href="https://github.com/rpodgorny/unionfs-fuse">https://github.com/rpodgorny/unionfs-fuse</a></li></ul><p>unionfs-fuse is more like unionfs, aufs, and overlayfs than mergerfsin that it offers overlay / copy-on-write (CoW) features. If you'rejust looking to create a union of filesystems and want flexibility infile/directory placement then mergerfs offers that whereasunionfs-fuse is more for overlaying read/write filesystems overread-only ones.</p><p>Since unionfs-fuse, as the name suggests, is a FUSE based technologyit can be used without elevated privileges that kernel solutions suchas unionfs, aufs, and overlayfs require.</p><h2 id="overlayfs">overlayfs</h2><ul><li><a href="https://docs.kernel.org/filesystems/overlayfs.html">https://docs.kernel.org/filesystems/overlayfs.html</a></li></ul><p>overlayfs is effectively the successor to unionfs, unionfs-fuse, andaufs and is widely used by Linux container platforms such as Docker andPodman. It was developed and is maintained by the same developer whocreated FUSE.</p><p>If your use case is layering a writable filesystem on top of read-onlyfilesystems then you should look first to overlayfs. Its feature sethowever is very different from mergerfs and solve different problems.</p><h2 id="raid0-jbod-span-drive-concatenation-striping">RAID0, JBOD, SPAN, drive concatenation, striping</h2><ul><li><a href="https://en.wikipedia.org/wiki/Standard_RAID_levels#RAID_0">RAID0</a></li><li><a href="https://en.wikipedia.org/wiki/Non-RAID_drive_architectures#JBOD">JBOD</a></li><li><a href="https://en.wikipedia.org/wiki/Non-RAID_drive_architectures#Concatenation_(SPAN,_BIG)">SPAN</a></li><li><a href="https://en.wikipedia.org/wiki/Data_striping">striping</a></li></ul><p>These are block device technologies which in some form aggregatedevices into what appears to be a singular device on which atraditional filesystem can be used. The filesystem has nounderstanding of the underlying block layout and should one of thoseunderlying devices fail or be removed the filesystem will be missingthat chunk which could contain critical information and the wholefilesystem may become unrecoverable. Even if the data from thefilesystem is recoverable it will take using specialized tooling to doso.</p><p>In contrast, with mergerfs you can format devices as one normallywould or take existing filesystems and then combine them in a pool toaggregate their storage. The failure of any one device will have noimpact on the other devices. The downside to mergerfs' technique isthe fact you don't actually have contiguous space as large as if youused those other technologies. Meaning you can't create a file greaterthan 1TB on a pool of 2 1TB filesystems.</p><h2 id="unraid">UnRAID</h2><ul><li><a href="https://unraid.net">https://unraid.net</a></li></ul><p>UnRAID is a full OS and offers a (FUSE based?) filesystem whichprovides a union of filesystems like mergerfs but with the addition oflive parity calculation and storage. Outside parity calculationsmergerfs offers more features and due to the lack of real-time paritycalculation can have higher peak performance. Some users also preferan open source solution.</p><p>For semi-static data mergerfs + <a href="http://www.snapraid.it">SnapRaid</a>provides a similar, but not real-time, solution.</p><h2 id="zfs">ZFS</h2><ul><li><a href="https://en.wikipedia.org/wiki/ZFS">https://en.wikipedia.org/wiki/ZFS</a></li></ul><p>mergerfs is very different from ZFS. mergerfs is intended to provideflexible pooling of arbitrary filesystems (local or remote), ofarbitrary sizes, and arbitrary filesystems. Particularly in <code>writeonce, read many</code> use cases such as bulk media storage. Where dataintegrity and backup is managed in other ways. In those use cases ZFScan introduce a number of costs and limitations as described<a href="http://louwrentius.com/the-hidden-cost-of-using-zfs-for-your-home-nas.html">here</a>,<a href="https://markmcb.com/2020/01/07/five-years-of-btrfs/">here</a>, and<a href="https://utcc.utoronto.ca/~cks/space/blog/solaris/ZFSWhyNoRealReshaping">here</a>.</p><h2 id="stablebits-drivepool">StableBit's DrivePool</h2><ul><li><a href="https://stablebit.com">https://stablebit.com</a></li></ul><p>DrivePool works only on Windows so not as common an alternative asother Linux solutions. If you want to use Windows then DrivePool is agood option. Functionally the two projects work a bitdifferently. DrivePool always writes to the filesystem with the mostfree space and later rebalances. mergerfs does not currently offerrebalance but chooses a branch at file/directory createtime. DrivePool's rebalancing can be done differently in any directoryand has file pattern matching to further customize thebehavior. mergerfs, not having rebalancing does not have thesefeatures, but similar features are planned for mergerfs v3. DrivePoolhas builtin file duplication which mergerfs does not natively support(but can be done via an external script.)</p><p>There are a lot of misc differences between the two projects but mostfeatures in DrivePool can be replicated with external tools incombination with mergerfs.</p><p>Additionally, DrivePool is a closed source commercial product vsmergerfs a ISC licensed open source project.</p><h2 id="plan9-binds">Plan9 binds</h2><ul><li><a href="https://en.wikipedia.org/wiki/Plan_9_from_Bell_Labs#Union_directories_and_namespaces">https://en.wikipedia.org/wiki/Plan_9_from_Bell_Labs#Union_directories_and_namespaces</a></li></ul><p>Plan9 has the native ability to bind multiple paths/filesystemstogether to create a setup similar to simplified unionfilesystem. Such bind mounts choose files in a "first found" in theorder they are listed similar to mergerfs' <code>ff</code> policy. Similar, whencreating a file it will be created on the first directory in theunion.</p><p>Plan 9 isn't a widely used OS so this comparison is mostly academic.</p>
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