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<h1 id="configuration-and-policies">Configuration and Policies</h1>
<h2 id="what-policies-should-i-use">What policies should I use?</h2>
<p>Unless you're doing something more niche the average user is probably
best off using <code>mfs</code> for <code>category.create</code>. It will spread files out
across your branches based on available space. Use <code>mspmfs</code> if you
want to try to colocate the data a bit more. You may want to use <code>lus</code>
if you prefer a slightly different distribution of data if you have a
mix of smaller and larger filesystems. Generally though <code>mfs</code>, <code>lus</code>,
or even <code>rand</code> are good for the general use case. If you are starting
with an imbalanced pool you can use the tool <strong>mergerfs.balance</strong> to
redistribute files across the pool.</p>
<p>If you really wish to try to colocate files based on directory you can
set <code>func.create</code> to <code>epmfs</code> or similar and <code>func.mkdir</code> to <code>rand</code> or
<code>eprand</code> depending on if you just want to colocate generally or on
specific branches. Either way the <em>need</em> to colocate is rare. For
instance: if you wish to remove the device regularly and want the data
to predictably be on that device or if you don't use backup at all and
don't wish to replace that data piecemeal. In which case using path
preservation can help but will require some manual
attention. Colocating after the fact can be accomplished using the
<strong>mergerfs.consolidate</strong> tool. If you don't need strict colocation
which the <code>ep</code> policies provide then you can use the <code>msp</code> based
policies which will walk back the path till finding a branch that
works.</p>
<p>Ultimately there is no correct answer. It is a preference or based on
some particular need. mergerfs is very easy to test and experiment
with. I suggest creating a test setup and experimenting to get a sense
of what you want.</p>
<p><code>epmfs</code> is the default <code>category.create</code> policy because <code>ep</code> policies
are not going to change the general layout of the branches. It won't
place files/dirs on branches that don't already have the relative
branch. So it keeps the system in a known state. It's much easier to
stop using <code>epmfs</code> or redistribute files around the filesystem than it
is to consolidate them back.</p>
<h2 id="what-settings-should-i-use">What settings should I use?</h2>
<p>Depends on what features you want. Generally speaking, there are no
"wrong" settings. All settings are performance or feature related. The
best bet is to read over the available options and choose what fits
your situation. If something isn't clear from the documentation please
reach out and the documentation will be improved.</p>
<p>That said, for the average person, the following should be fine:</p>
<p><code>cache.files=off,dropcacheonclose=true,category.create=mfs</code></p>
<h2 id="why-are-all-my-files-ending-up-on-1-filesystem">Why are all my files ending up on 1 filesystem?!</h2>
<p>Did you start with empty filesystems? Did you explicitly configure a
<code>category.create</code> policy? Are you using an <code>existing path</code> / <code>path
preserving</code> policy?</p>
<p>The default create policy is <code>epmfs</code>. That is a path preserving
algorithm. With such a policy for <code>mkdir</code> and <code>create</code> with a set of
empty filesystems it will select only 1 filesystem when the first
directory is created. Anything, files or directories, created in that
first directory will be placed on the same branch because it is
preserving paths.</p>
<p>This catches a lot of new users off guard but changing the default
would break the setup for many existing users and this policy is the
safest policy as it will not change the general layout of the existing
filesystems. If you do not care about path preservation and wish your
files to be spread across all your filesystems change to <code>mfs</code> or
similar policy as described above. If you do want path preservation
you'll need to perform the manual act of creating paths on the
filesystems you want the data to land on before transferring your
data. Setting <code>func.mkdir=epall</code> can simplify managing path
preservation for <code>create</code>. Or use <code>func.mkdir=rand</code> if you're
interested in just grouping directory content by filesystem.</p>


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