3.7 KiB
Configuration and Policies
What policies should I use?
Unless you're doing something more niche the average user is probably
best off using mfs
for category.create
. It will spread files out
across your branches based on available space. Use mspmfs
if you
want to try to colocate the data a bit more. You may want to use lus
if you prefer a slightly different distribution of data if you have a
mix of smaller and larger filesystems. Generally though mfs
, lus
,
or even rand
are good for the general use case. If you are starting
with an imbalanced pool you can use the tool mergerfs.balance to
redistribute files across the pool.
If you really wish to try to colocate files based on directory you can
set func.create
to epmfs
or similar and func.mkdir
to rand
or
eprand
depending on if you just want to colocate generally or on
specific branches. Either way the need 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
mergerfs.consolidate tool. If you don't need strict colocation
which the ep
policies provide then you can use the msp
based
policies which will walk back the path till finding a branch that
works.
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.
epmfs
is the default category.create
policy because ep
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 epmfs
or redistribute files around the filesystem than it
is to consolidate them back.
What settings should I use?
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.
That said, for the average person, the following should be fine:
cache.files=off,dropcacheonclose=true,category.create=mfs
Why are all my files ending up on 1 filesystem?!
Did you start with empty filesystems? Did you explicitly configure a
category.create
policy? Are you using an existing path
/ path preserving
policy?
The default create policy is epmfs
. That is a path preserving
algorithm. With such a policy for mkdir
and create
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.
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 mfs
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 func.mkdir=epall
can simplify managing path
preservation for create
. Or use func.mkdir=rand
if you're
interested in just grouping directory content by filesystem.