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<span class="md-nav__icon md-icon"></span> </label> <a href="." class="md-nav__link md-nav__link--active"> <span class="md-ellipsis"> Home </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="#features" class="md-nav__link"> <span class="md-ellipsis"> Features </span> </a> </li> <li class="md-nav__item"> <a href="#non-features" class="md-nav__link"> <span class="md-ellipsis"> Non-features </span> </a> </li> <li class="md-nav__item"> <a href="#how-it-works" class="md-nav__link"> <span class="md-ellipsis"> How it works </span> </a> <nav class="md-nav" aria-label="How it works"> <ul class="md-nav__list"> <li class="md-nav__item"> <a href="#visualization" class="md-nav__link"> <span class="md-ellipsis"> Visualization </span> </a> </li> </ul> </nav> </li> </ul> </nav> </li>
<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 md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type="checkbox" id="__nav_4" > <label class="md-nav__link" for="__nav_4" id="__nav_4_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_4_label" aria-expanded="false"> <label class="md-nav__title" for="__nav_4"> <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/terminology/" class="md-nav__link"> <span class="md-ellipsis"> Terminology </span>
</a> </li>
<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/" class="md-nav__link"> <span class="md-ellipsis"> Error Handling </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"> <a href="project_comparisons/" class="md-nav__link"> <span class="md-ellipsis"> Project Comparisons </span>
</a> </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 md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type="checkbox" id="__nav_14" > <label class="md-nav__link" for="__nav_14" id="__nav_14_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_14_label" aria-expanded="false"> <label class="md-nav__title" for="__nav_14"> <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/limit_drive_spinup/" class="md-nav__link"> <span class="md-ellipsis"> Limiting drive spinup </span>
</a> </li>
</ul> </nav> </li>
<li class="md-nav__item"> <a href="related_projects/" class="md-nav__link"> <span class="md-ellipsis"> Related Projects </span>
</a> </li>
<li class="md-nav__item"> <a href="media_and_publicity/" class="md-nav__link"> <span class="md-ellipsis"> Media and Publicity </span>
</a> </li>
<li class="md-nav__item"> <a href="support/" class="md-nav__link"> <span class="md-ellipsis"> Support </span>
</a> </li>
<li class="md-nav__item"> <a href="sponsorship_and_donations/" class="md-nav__link"> <span class="md-ellipsis"> Sponsorship and Donations </span>
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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="#features" class="md-nav__link"> <span class="md-ellipsis"> Features </span> </a> </li> <li class="md-nav__item"> <a href="#non-features" class="md-nav__link"> <span class="md-ellipsis"> Non-features </span> </a> </li> <li class="md-nav__item"> <a href="#how-it-works" class="md-nav__link"> <span class="md-ellipsis"> How it works </span> </a> <nav class="md-nav" aria-label="How it works"> <ul class="md-nav__list"> <li class="md-nav__item"> <a href="#visualization" class="md-nav__link"> <span class="md-ellipsis"> Visualization </span> </a> </li> </ul> </nav> </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/tree/master/mkdocs/docs/index.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/tree/master/mkdocs/docs/index.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="mergerfs-a-featureful-union-filesystem">mergerfs - a featureful union filesystem</h1><p><strong>mergerfs</strong> is a<a href="https://en.wikipedia.org/wiki/Filesystem_in_Userspace">FUSE</a> based<a href="https://en.wikipedia.org/wiki/Union_mount">union filesystem</a> gearedtowards simplifying storage and management of files across numerouscommodity storage devices. It is similar to <strong>mhddfs</strong>, <strong>unionfs</strong>,and <strong>aufs</strong>.</p><h2 id="features">Features</h2><ul><li>Logicially combine numerous filesystems/paths into a single mount point</li><li>Combine paths of the same or different filesystems</li><li>Ability to add or remove filesystems/paths without impacting the rest of the data</li><li>Unaffected by individual filesystem failure</li><li>Configurable file selection and creation placement</li><li>Works with filesystems of any size</li><li>Works with filesystems of almost any type</li><li>Ignore read-only filesystems when creating files</li><li>Hard link copy-on-write / CoW</li><li>Runtime configurable</li><li>Support for extended attributes (xattrs)</li><li>Support for file attributes (chattr)</li><li>Support for POSIX ACLs</li></ul><h2 id="non-features">Non-features</h2><ul><li>Read/write overlay on top of readonly filesystem like OverlayFS</li><li>File whiteout</li><li>RAID like parity calculation</li><li>Redundency</li><li>Splitting of files across branches</li></ul><h2 id="how-it-works">How it works</h2><p>mergerfs logically merges multiple filesystem paths together. It actsas a proxy to the underlying filesystem paths. Combining thebehaviors of some functions and being a selector for others.</p><p>When the contents of a directory are requested mergerfs combines thelist of files from each directory, deduplicating entries, and returnsthat list.</p><p>When a file or directory is created a policy is first run to determinewhich branch will be selected for the creation.</p><p>For functions which chant attributes or remove the file the behaviormay be applied to all instances found.</p><p>Read more about <a href="config/functions_categories_and_policies/">policies here</a>.</p><h3 id="visualization">Visualization</h3><div class="language-text highlight"><pre><span></span><code><span id="__span-0-1"><a id="__codelineno-0-1" name="__codelineno-0-1" href="#__codelineno-0-1"></a>A + B = C</span><span id="__span-0-2"><a id="__codelineno-0-2" name="__codelineno-0-2" href="#__codelineno-0-2"></a>/disk1 /disk2 /merged</span><span id="__span-0-3"><a id="__codelineno-0-3" name="__codelineno-0-3" href="#__codelineno-0-3"></a>| | |</span><span id="__span-0-4"><a id="__codelineno-0-4" name="__codelineno-0-4" href="#__codelineno-0-4"></a>+-- /dir1 +-- /dir1 +-- /dir1</span><span id="__span-0-5"><a id="__codelineno-0-5" name="__codelineno-0-5" href="#__codelineno-0-5"></a>| | | | | |</span><span id="__span-0-6"><a id="__codelineno-0-6" name="__codelineno-0-6" href="#__codelineno-0-6"></a>| +-- file1 | +-- file2 | +-- file1</span><span id="__span-0-7"><a id="__codelineno-0-7" name="__codelineno-0-7" href="#__codelineno-0-7"></a>| | +-- file3 | +-- file2</span><span id="__span-0-8"><a id="__codelineno-0-8" name="__codelineno-0-8" href="#__codelineno-0-8"></a>+-- /dir2 | | +-- file3</span><span id="__span-0-9"><a id="__codelineno-0-9" name="__codelineno-0-9" href="#__codelineno-0-9"></a>| | +-- /dir3 |</span><span id="__span-0-10"><a id="__codelineno-0-10" name="__codelineno-0-10" href="#__codelineno-0-10"></a>| +-- file4 | +-- /dir2</span><span id="__span-0-11"><a id="__codelineno-0-11" name="__codelineno-0-11" href="#__codelineno-0-11"></a>| +-- file5 | |</span><span id="__span-0-12"><a id="__codelineno-0-12" name="__codelineno-0-12" href="#__codelineno-0-12"></a>+-- file6 | +-- file4</span><span id="__span-0-13"><a id="__codelineno-0-13" name="__codelineno-0-13" href="#__codelineno-0-13"></a> |</span><span id="__span-0-14"><a id="__codelineno-0-14" name="__codelineno-0-14" href="#__codelineno-0-14"></a> +-- /dir3</span><span id="__span-0-15"><a id="__codelineno-0-15" name="__codelineno-0-15" href="#__codelineno-0-15"></a> | |</span><span id="__span-0-16"><a id="__codelineno-0-16" name="__codelineno-0-16" href="#__codelineno-0-16"></a> | +-- file5</span><span id="__span-0-17"><a id="__codelineno-0-17" name="__codelineno-0-17" href="#__codelineno-0-17"></a> |</span><span id="__span-0-18"><a id="__codelineno-0-18" name="__codelineno-0-18" href="#__codelineno-0-18"></a> +-- file6</span></code></pre></div>
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