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<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>
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<li class="md-nav__item"> <a href="../config/deprecated_options/" class="md-nav__link"> <span class="md-ellipsis"> Deprecated Options </span>
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<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>
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<li class="md-nav__item"> <a href="../config/func_readdir/" class="md-nav__link"> <span class="md-ellipsis"> func.readdir </span>
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<li class="md-nav__item"> <a href="../config/rename_and_link/" class="md-nav__link"> <span class="md-ellipsis"> rename and link </span>
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</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>
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<li class="md-nav__item"> <a href="../error_handling_and_logging/" class="md-nav__link"> <span class="md-ellipsis"> Error Handling and Logging </span>
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</a> </li>
<li class="md-nav__item"> <a href="../remote_filesystems/" class="md-nav__link"> <span class="md-ellipsis"> Remote Filesystems </span>
</a> </li>
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</a> </li>
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<li class="md-nav__item"> <a href="../performance/" class="md-nav__link"> <span class="md-ellipsis"> Tweaking Performance </span>
</a> </li>
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</a> </li>
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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"> Usage Patterns </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="#tiered-cache" class="md-nav__link"> <span class="md-ellipsis"> tiered cache </span> </a> <nav class="md-nav" aria-label="tiered cache"> <ul class="md-nav__list"> <li class="md-nav__item"> <a href="#time-based-expiring" class="md-nav__link"> <span class="md-ellipsis"> time based expiring </span> </a> </li> <li class="md-nav__item"> <a href="#percentage-full-expiring" class="md-nav__link"> <span class="md-ellipsis"> percentage full expiring </span> </a> </li> </ul> </nav> </li> </ul> </nav> </li>
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<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>
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<li class="md-nav__item"> <a href="../faq/recommendations_and_warnings/" class="md-nav__link"> <span class="md-ellipsis"> Recommendations and Warnings </span>
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<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>
<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>
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<li class="md-nav__item"> <a href="../related_projects/" class="md-nav__link"> <span class="md-ellipsis"> Related Projects </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="#tiered-cache" class="md-nav__link"> <span class="md-ellipsis"> tiered cache </span> </a> <nav class="md-nav" aria-label="tiered cache"> <ul class="md-nav__list"> <li class="md-nav__item"> <a href="#time-based-expiring" class="md-nav__link"> <span class="md-ellipsis"> time based expiring </span> </a> </li> <li class="md-nav__item"> <a href="#percentage-full-expiring" class="md-nav__link"> <span class="md-ellipsis"> percentage full expiring </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/edit/master/mkdocs/docs/usage_patterns.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/usage_patterns.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="usage-patterns">Usage Patterns</h1><h2 id="tiered-cache">tiered cache</h2><p>Some storage technologies support what is called "tiered" caching. Theplacing of smaller, faster storage as a transparent cache to larger,slower storage. NVMe, SSD, Optane in front of traditional HDDs forinstance.</p><p>mergerfs does not natively support any sort of tiered caching. Mostusers have no use for such a feature and its inclusion wouldcomplicate the code as it exists today. However, there are a fewsituations where a cache filesystem could help with a typical mergerfssetup.</p><ol><li>Fast network, slow filesystems, many readers: You've a 10+Gbps network with many readers and your regular filesystems can't keep up.</li><li>Fast network, slow filesystems, small'ish bursty writes: You have a 10+Gbps network and wish to transfer amounts of data less than your cache filesystem but wish to do so quickly and the time between bursts is long enough to migrate data.</li></ol><p>With #1 it's arguable if you should be using mergerfs at all. A RAIDlevel that can aggregate performance or using higher performancestorage would probably be the better solution. If you're going to usemergerfs there are other tactics that may help: spreading the dataacross filesystems (see the mergerfs.dup tool) and setting<code>func.open=rand</code>, using <code>symlinkify</code>, or using dm-cache or a similartechnology to add tiered cache to the underlying device itself.</p><p>With #2 one could use a block cache solution as available via LVM anddm-cache but there is another solution which requires only mergerfs, ascript to move files around, and a cron job to run said script.</p><ul><li>Create two mergerfs pools. One which includes just the <strong>slow</strong> branches and one which has both the <strong>fast</strong> branches (SSD,NVME,etc.) and <strong>slow</strong> branches. The <strong>base</strong> pool and the <strong>cache</strong> pool.</li><li>The <strong>cache</strong> pool should have the cache branches listed first in the branch list in order to to make it easier to prioritize them.</li><li>The best <code>create</code> policies to use for the <strong>cache</strong> pool would probably be <code>ff</code>, <code>lus</code>, or <code>lfs</code>. The latter two under the assumption that the cache filesystem(s) are far smaller than the backing filesystems.</li><li>You can also set the <strong>slow</strong> filesystems mode to <code>NC</code> which would give you the ability to use other <code>create</code> policies though that'd mean if the cache filesystems fill you'd get "out of space" errors. This however may be good as it would indicate the script moving files around is not configured properly.</li><li>Set your programs to use the <strong>cache</strong> pool.</li><li>Configure the <strong>base</strong> pool with the <code>create</code> policy you would like to lay out files as you like.</li><li>Save one of the below scripts or create your own. The script's responsibility is to move files from the <strong>cache</strong> branches (not pool) to the <strong>base</strong> pool.</li><li>Use <code>cron</code> (as root) to schedule the command at whatever frequency is appropriate for your workflow.</li></ul><h3 id="time-based-expiring">time based expiring</h3><p>Move files from cache filesystem to base pool which have an accesstime older than the supplied number of days. Replace <code>-atime</code> with<code>-amin</code> in the script if you want minutes rather than days.</p><p><strong>NOTE:</strong> The arguments to these scripts include the cache<strong>filesystem</strong> itself. Not the pool with the cache filesystem. Youcould have data loss if the source is the cache pool.</p><p><a href="https://github.com/trapexit/mergerfs/blob/latest-release/tools/mergerfs.time-based-mover?raw=1">mergerfs.time-based-mover</a></p><p>Download:<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>curl -o /usr/local/bin/mergerfs.time-based-mover https://raw.githubusercontent.com/trapexit/mergerfs/refs/heads/latest-release/tools/mergerfs.time-based-mover</span></code></pre></div></p><p>crontab entry:<div class="language-text highlight"><pre><span></span><code><span id="__span-1-1"><a id="__codelineno-1-1" name="__codelineno-1-1" href="#__codelineno-1-1"></a># m h dom mon dow command</span><span id="__span-1-2"><a id="__codelineno-1-2" name="__codelineno-1-2" href="#__codelineno-1-2"></a>0 * * * * /usr/local/bin/mergerfs.time-based-mover /mnt/ssd/cache00 /mnt/base-pool 1</span></code></pre></div></p><p>If you have more than one cache filesystem then simply add a cronentry for each.</p><p>If you want to only move files from a subdirectory then use thesubdirectories. <code>/mnt/ssd/cache00/foo</code> and <code>/mnt/base-pool/foo</code>respectively.</p><h3 id="percentage-full-expiring">percentage full expiring</h3><p>While the cache filesystem's percentage full is above the providedvalue move the oldest file from the cache filesystem to the base pool.</p><p><strong>NOTE:</strong> The arguments to these scripts include the cache<strong>filesystem</strong> itself. Not the pool with the cache filesystem. Youcould have data loss if the source is the cache pool.</p><p><a href="https://github.com/trapexit/mergerfs/blob/latest-release/tools/mergerfs.percent-full-mover?raw=1">mergerfs.percent-full-mover</a></p><p>Download:<div class="language-text highlight"><pre><span></span><code><span id="__span-2-1"><a id="__codelineno-2-1" name="__codelineno-2-1" href="#__codelineno-2-1"></a>curl -o /usr/local/bin/mergerfs.percent-full-mover https://raw.githubusercontent.com/trapexit/mergerfs/refs/heads/latest-release/tools/mergerfs.percent-full-mover</span></code></pre></div></p><p>crontab entry:<div class="language-text highlight"><pre><span></span><code><span id="__span-3-1"><a id="__codelineno-3-1" name="__codelineno-3-1" href="#__codelineno-3-1"></a># m h dom mon dow command</span><span id="__span-3-2"><a id="__codelineno-3-2" name="__codelineno-3-2" href="#__codelineno-3-2"></a>0 * * * * /usr/local/bin/mergerfs.percent-full-mover /mnt/ssd/cache00 /mnt/base-pool 80</span></code></pre></div></p><p>If you have more than one cache filesystem then simply add a cronentry for each.</p><p>If you want to only move files from a subdirectory then use thesubdirectories. <code>/mnt/ssd/cache00/foo</code> and <code>/mnt/base-pool/foo</code>respectively.</p>
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