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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="#can-mergerfs-be-used-with-filesystems-which-already-have-data" class="md-nav__link"> <span class="md-ellipsis"> Can mergerfs be used with filesystems which already have data? </span> </a> </li> <li class="md-nav__item"> <a href="#can-filesystems-be-removed-from-the-pool-without-affecting-them" class="md-nav__link"> <span class="md-ellipsis"> Can filesystems be removed from the pool without affecting them? </span> </a> </li> <li class="md-nav__item"> <a href="#can-mergerfs-be-removed-without-affecting-the-data" class="md-nav__link"> <span class="md-ellipsis"> Can mergerfs be removed without affecting the data? </span> </a> </li> <li class="md-nav__item"> <a href="#can-filesystems-be-moved-to-another-pool" class="md-nav__link"> <span class="md-ellipsis"> Can filesystems be moved to another pool? </span> </a> </li> <li class="md-nav__item"> <a href="#can-filesystems-be-part-of-multiple-pools" class="md-nav__link"> <span class="md-ellipsis"> Can filesystems be part of multiple pools? </span> </a> </li> <li class="md-nav__item"> <a href="#how-do-i-migrate-data-into-or-out-of-the-pool-when-addingremoving-filesystems" class="md-nav__link"> <span class="md-ellipsis"> How do I migrate data into or out of the pool when adding/removing filesystems? </span> </a> </li> <li class="md-nav__item"> <a href="#how-do-i-remove-a-filesystem-but-keep-the-data-in-the-pool" class="md-nav__link"> <span class="md-ellipsis"> How do I remove a filesystem but keep the data in the pool? </span> </a> </li> <li class="md-nav__item"> <a href="#can-filesystems-still-be-used-directly-outside-of-mergerfs-while-pooled" class="md-nav__link"> <span class="md-ellipsis"> Can filesystems still be used directly? Outside of mergerfs while pooled? </span> </a> </li> </ul> </nav> </li>
<li class="md-nav__item"> <a href="../configuration_and_policies/" class="md-nav__link"> <span class="md-ellipsis"> Configuration and Policies </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="#can-mergerfs-be-used-with-filesystems-which-already-have-data" class="md-nav__link"> <span class="md-ellipsis"> Can mergerfs be used with filesystems which already have data? </span> </a> </li> <li class="md-nav__item"> <a href="#can-filesystems-be-removed-from-the-pool-without-affecting-them" class="md-nav__link"> <span class="md-ellipsis"> Can filesystems be removed from the pool without affecting them? </span> </a> </li> <li class="md-nav__item"> <a href="#can-mergerfs-be-removed-without-affecting-the-data" class="md-nav__link"> <span class="md-ellipsis"> Can mergerfs be removed without affecting the data? </span> </a> </li> <li class="md-nav__item"> <a href="#can-filesystems-be-moved-to-another-pool" class="md-nav__link"> <span class="md-ellipsis"> Can filesystems be moved to another pool? </span> </a> </li> <li class="md-nav__item"> <a href="#can-filesystems-be-part-of-multiple-pools" class="md-nav__link"> <span class="md-ellipsis"> Can filesystems be part of multiple pools? </span> </a> </li> <li class="md-nav__item"> <a href="#how-do-i-migrate-data-into-or-out-of-the-pool-when-addingremoving-filesystems" class="md-nav__link"> <span class="md-ellipsis"> How do I migrate data into or out of the pool when adding/removing filesystems? </span> </a> </li> <li class="md-nav__item"> <a href="#how-do-i-remove-a-filesystem-but-keep-the-data-in-the-pool" class="md-nav__link"> <span class="md-ellipsis"> How do I remove a filesystem but keep the data in the pool? </span> </a> </li> <li class="md-nav__item"> <a href="#can-filesystems-still-be-used-directly-outside-of-mergerfs-while-pooled" class="md-nav__link"> <span class="md-ellipsis"> Can filesystems still be used directly? Outside of mergerfs while pooled? </span> </a> </li> </ul> </nav> </div> </div> </div> <div class="md-content" data-md-component="content"> <article class="md-content__inner md-typeset">
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<h1 id="usage-and-functionality">Usage and Functionality</h1><h2 id="can-mergerfs-be-used-with-filesystems-which-already-have-data">Can mergerfs be used with filesystems which already have data?</h2><p>Yes. mergerfs is really just a proxy and does <strong>NOT</strong> interfere withthe normal form or function of the filesystems, mounts, or paths itmanages. It literally is interacting with your filesystems as anyother application does. It can not do anything that any other randompiece of software can't do.</p><p>mergerfs is <strong>not</strong> a traditional filesystem that takes control overthe underlying disk or block device. mergerfs is <strong>not</strong> RAID. It does<strong>not</strong> manipulate the data that passes through it. It does <strong>not</strong>shard data across filesystems. It only shards some <strong>behavior</strong> andaggregates others.</p><h2 id="can-filesystems-be-removed-from-the-pool-without-affecting-them">Can filesystems be removed from the pool without affecting them?</h2><p>Yes. See previous question's answer.</p><h2 id="can-mergerfs-be-removed-without-affecting-the-data">Can mergerfs be removed without affecting the data?</h2><p>Yes. See the previous question's answer.</p><h2 id="can-filesystems-be-moved-to-another-pool">Can filesystems be moved to another pool?</h2><p>Yes. See the previous question's answer.</p><h2 id="can-filesystems-be-part-of-multiple-pools">Can filesystems be part of multiple pools?</h2><p>Yes.</p><h2 id="how-do-i-migrate-data-into-or-out-of-the-pool-when-addingremoving-filesystems">How do I migrate data into or out of the pool when adding/removing filesystems?</h2><p>There is no need to do so. See the previous questions.</p><h2 id="how-do-i-remove-a-filesystem-but-keep-the-data-in-the-pool">How do I remove a filesystem but keep the data in the pool?</h2><p>Nothing special needs to be done. Remove the branch from mergerfs'config and copy (rsync) the data from the removed filesystem into thepool. The same as if it were you transferring data from one filesystemto another.</p><p>If you wish to continue using the pool with all data available whileperforming the transfer simply create a temporary pool without thebranch in question and then copy the data from the branch to thetemporary pool. It would probably be a good idea to set the branchmode to <code>RO</code> prior to doing this to ensure no new content is writtento the filesystem while performing the copy. However, it is typicallygood practice to run rsync or rclone again after the first copyfinishes to ensure nothing is left behind.</p><p>NOTE: Above recommends to "copy" rather than "move" because you wantto ensure that your data is transferred before wiping the drive orfilesystem.</p><h2 id="can-filesystems-still-be-used-directly-outside-of-mergerfs-while-pooled">Can filesystems still be used directly? Outside of mergerfs while pooled?</h2><p>Yes, <a href="https://en.wikipedia.org/wiki/Out-of-band">out-of-band</a>interaction is generally fine. Remember that mergerfs is a userlandapplication so any interaction with the underlying filesystem is thesame as multiple normal applications interacting. However, it is notrecommended to write to the same file from within the pool and fromwithout at the same time. Especially if using page caching(<code>cache.files!=off</code>) or writeback caching(<code>cache.writeback=true</code>). That said this risk is really not differentfrom the risk of two applications writing to the same file undernormal conditions.</p><p>Keep in mind that if out-of-band changes are made while alsoleveraging any caching of the filesystem layout such as with<code>cache.entry</code>, <code>cache.negative_entry</code>, <code>cache.attr</code>, <code>cache.symlinks</code>,or <code>cache.readdir</code> you may experience temporary inconsistency till thecache expires. mergerfs is not actively watching all branches forchanges and the kernel will have no way to know anything changed so asto clear or ignore the cache. This is the same issue you can have with<a href="../../remote_filesystems/">remote filesystems</a>.</p>
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