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@ -214,6 +214,10 @@ This means files, when renamed or linked, will stay on the same |
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filesystem. |
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(default: false) |
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.IP \[bu] 2 |
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\f[B]export-support=BOOL\f[R]: Sets a low-level FUSE feature intended to |
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indicate the filesystem can support being exported via NFS. |
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(default: true) |
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.IP \[bu] 2 |
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\f[B]security_capability=BOOL\f[R]: If false return ENOATTR when xattr |
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security.capability is queried. |
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(default: true) |
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@ -547,7 +551,7 @@ Most software does not to care what the values are but those that do |
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often break if a value changes unexpectedly. |
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The tool \f[C]find\f[R] will abort a directory walk if it sees a |
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directory inode change. |
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NFS will return stale handle errors if the inode changes out of band. |
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NFS can return stale handle errors if the inode changes out of band. |
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File dedup tools will usually leverage device ids and inodes as a |
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shortcut in searching for duplicate files and would resort to full file |
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comparisons should it find different inode values. |
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@ -837,6 +841,26 @@ If set to \f[C]git\f[R] it will only perform the hack when the path in |
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question includes \f[C]/.git/\f[R]. |
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\f[C]all\f[R] will result it applying anytime a read-only file which is |
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empty is opened for writing. |
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.SS export-support |
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.PP |
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In theory this flag should not be exposed to the end user. |
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It is a low-level FUSE flag which indicates whether or not the kernel |
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can send certain kinds of messages to it for the purposes of using with |
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NFS. |
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mergerfs does support these messages but due to a possible bug in the |
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Linux kernel this option needs to be configurable. |
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As it turns out at least certain versions of NFS can still work when |
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disabled and no longer triggers the bug. |
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.PP |
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While it may be safe to default this setting to \f[C]false\f[R] in an |
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abundance of caution it is being left enabled by default. |
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.PP |
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Given that this flag is set when the FUSE connection is first initiated |
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it is not possible to change during run time. |
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.PP |
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See Kernel Issues & |
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Bugs (https://github.com/trapexit/mergerfs/wiki/Kernel-Issues-&-Bugs) |
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for more details. |
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.SH FUNCTIONS, CATEGORIES and POLICIES |
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.PP |
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The POSIX filesystem API is made up of a number of functions. |
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@ -2375,14 +2399,9 @@ Use \f[C]cache.files=off\f[R] and/or \f[C]dropcacheonclose=true\f[R]. |
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See the section on page caching. |
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.SS NFS clients returning ESTALE / Stale file handle |
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.PP |
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NFS does not like out of band changes. |
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That is especially true of inode values. |
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.PP |
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Be sure to use the following options: |
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.IP \[bu] 2 |
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noforget |
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.IP \[bu] 2 |
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inodecalc=path-hash |
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NFS generally does not like out of band changes. |
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Take a look at the section on NFS in the #remote-filesystems for more |
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details. |
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.SS rtorrent fails with ENODEV (No such device) |
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.PP |
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Be sure to set \f[C]cache.files=partial|full|auto-full|per-processe\f[R] |
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@ -2539,6 +2558,127 @@ There might be a hack to work around this (make mergerfs read the |
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would be limited to Linux and the /etc/group DB. |
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Preferably users would mount in the host group file into the containers |
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or use a standard shared user & groups technology like NIS or LDAP. |
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.SH Remote Filesystems |
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.PP |
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Many users ask about compatibility with remote filesystems. |
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This section is to describe any known issues or quirks when using |
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mergerfs with common remote filesystems. |
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.PP |
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Keep in mind that, like with caching, it is not a good idea to change |
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the contents of the remote filesystem |
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out-of-band (https://en.wikipedia.org/wiki/Out-of-band). |
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Meaning that you really shouldn\[cq]t change the contents of the |
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underlying filesystems or mergerfs on the server hosting the remote |
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filesystem. |
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Doing so can lead to weird behavior, inconsistency, errors, and even |
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data corruption should multiple programs try to write or read the same |
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data at the same time. |
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This isn\[cq]t to say you can\[cq]t do it or that data corruption is |
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likely but it \f[I]could\f[R] happen. |
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It is better to always use the remote filesystem. |
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Even on the machine serving it. |
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.SS NFS |
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.PP |
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NFS (https://en.wikipedia.org/wiki/Network_File_System) is a common |
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remote filesystem on Unix/POSIX systems. |
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Due to how NFS works there are some settings which need to be set in |
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order for mergerfs to work with it. |
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.PP |
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It should be noted that NFS and FUSE (the technology mergerfs uses) do |
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not work perfectly with one another due to certain design choices in |
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FUSE (and mergerfs.) Due to these issues it is generally recommended to |
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use SMB when possible till situations change. |
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That said issues should still be reported. |
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NFS is not really recommended but it isn\[cq]t unsupported. |
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.PP |
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When exporting mergerfs via NFS ensure to set the following config: * |
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noforget * inodecalc=path-hash * export-support=false (only available in |
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v2.40.0 and above) |
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.PP |
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\f[C]noforget\f[R] is needed because NFS uses the |
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\f[C]name_to_handle_at\f[R] and \f[C]open_by_handle_at\f[R] functions |
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which allow a program to keep a reference to a file without technically |
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having it open in the typical sense. |
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The problem is that FUSE has no way to know that NFS has a handle that |
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it will later use to open the file again. |
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As a result it is possible for the kernel to tell mergerfs to forget |
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about the node and should NFS ever ask for that node\[cq]s details in |
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the future it would have nothing to respond with. |
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Keeping nodes around forever is not ideal but at the moment the only way |
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to manage the situation. |
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.PP |
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\f[C]inodecalc=path-hash\f[R] is needed because NFS is sensitive to |
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out-of-band changes. |
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FUSE doesn\[cq]t care if a file\[cq]s inode value changes but NFS, being |
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stateful, does. |
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So if you used the default inode calculation algorithm then it is |
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possible that if you changed a file or updated a directory the file |
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mergerfs will use will be on a different branch and therefore the inode |
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would change. |
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This isn\[cq]t an ideal solution and others are being considered but it |
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works for most situations. |
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It might be possible to leave the default value of \f[C]hybrid-hash\f[R] |
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if \f[C]export-support=false\f[R] but it hasn\[cq]t been fully tested |
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yet. |
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.PP |
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\f[C]export-support=false\f[R] is a low-level FUSE option that is needed |
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as a workaround to a Linux kernel bug. |
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Technically this option should be set to \f[C]true\f[R] when expecting |
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to use mergerfs with NFS but it turns out that at least some versions of |
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NFS work when not enabled. |
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At the moment it is unclear if this has any negative side effects but |
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when disabled NFS appears to work alright and the kernel no longer sends |
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invalid requests. |
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When the issue is resolved in the kernel these docs will be updated with |
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appropriate details. |
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.PP |
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Also see Kernel Issues & |
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Bugs (https://github.com/trapexit/mergerfs/wiki/Kernel-Issues-&-Bugs) |
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for more details. |
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.SS SMB / CIFS |
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.PP |
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SMB (https://en.wikipedia.org/wiki/Server_Message_Block) is a protocol |
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most used by Microsoft Windows systems to share file shares, printers, |
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etc. |
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However, due to the popularity for Windows, it is also supported on many |
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other platforms including Linux. |
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The most popular way of supporting SMB on Linux is via the software |
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Samba. |
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.PP |
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Samba (https://en.wikipedia.org/wiki/Samba_(software)), and other ways |
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of serving Linux filesystems, via SMB should work fine with mergerfs. |
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The services do not tend to use the same technologies which NFS uses and |
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therefore don\[cq]t have the same issues. |
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There should not be an special settings required to use mergerfs with |
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Samba. |
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However, CIFSD (https://en.wikipedia.org/wiki/CIFSD) and other programs |
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have not been extensively tested. |
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If you use mergerfs with CIFSD or other SMB servers please submit your |
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experiences so these docs can be updated. |
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.SS SSHFS |
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.PP |
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SSHFS (https://en.wikipedia.org/wiki/SSHFS) is a FUSE filesystem |
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leveraging SSH as the connection and transport layer. |
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While often simpler to setup when compared to NFS or Samba the |
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performance can be lacking and the project is very much in maintenance |
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mode. |
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.PP |
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There are no known issues using sshfs with mergerfs. |
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You may want to use the following arguments to improve performance but |
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your millage may vary. |
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.IP \[bu] 2 |
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\f[C]-o Ciphers=arcfour\f[R] |
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.IP \[bu] 2 |
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\f[C]-o Compression=no\f[R] |
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.PP |
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More info can be found |
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here (https://ideatrash.net/2016/08/odds-and-ends-optimizing-sshfs-moving.html). |
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.SS Other |
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.PP |
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There are other remote filesystems but none popularly used to serve |
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mergerfs. |
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If you use something not listed above feel free to reach out and I will |
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add it to the list. |
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.SH FAQ |
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.SS How well does mergerfs scale? Is it \[lq]production ready?\[rq] |
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.PP |
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@ -2780,8 +2920,8 @@ executable bit set. |
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A common mistake by users new to Linux is to \f[C]chmod -R 644\f[R] when |
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they should have \f[C]chmod -R u=rwX,go=rX\f[R]. |
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.PP |
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If using a network filesystem such as NFS, SMB, CIFS (Samba) be sure to |
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pay close attention to anything regarding permissioning and users. |
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If using a network filesystem such as NFS or SMB (Samba) be sure to pay |
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close attention to anything regarding permissioning and users. |
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Root squashing and user translation for instance has bitten a few |
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mergerfs users. |
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Some of these also affect the use of mergerfs from container platforms |
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@ -2906,33 +3046,14 @@ mergerfs uses available space for statfs calculations. |
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If you\[cq]ve reserved space for root then it won\[cq]t show up. |
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.PP |
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You can remove the reserve by running: \f[C]tune2fs -m 0 <device>\f[R] |
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.SS Can mergerfs mounts be exported over NFS? |
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.PP |
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Yes, however if you do anything which may changes files out of band |
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(including for example using the \f[C]newest\f[R] policy) it will result |
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in \[lq]stale file handle\[rq] errors unless properly setup. |
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.PP |
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Be sure to use the following options: |
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.IP \[bu] 2 |
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noforget |
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.IP \[bu] 2 |
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inodecalc=path-hash |
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.SS Can mergerfs mounts be exported over Samba / SMB? |
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.PP |
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Yes. |
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While some users have reported problems it appears to always be related |
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to how Samba is setup in relation to permissions. |
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.SS Can mergerfs mounts be used over SSHFS? |
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.PP |
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Yes. |
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.SS I notice massive slowdowns of writes when enabling cache.files. |
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.PP |
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When file caching is enabled in any form (\f[C]cache.files!=off\f[R] or |
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\f[C]direct_io=false\f[R]) it will issue \f[C]getxattr\f[R] requests for |
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\f[C]security.capability\f[R] prior to \f[I]every single write\f[R]. |
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When file caching is enabled in any form (\f[C]cache.files!=off\f[R]) it |
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will issue \f[C]getxattr\f[R] requests for \f[C]security.capability\f[R] |
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prior to \f[I]every single write\f[R]. |
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This will usually result in a performance degradation, especially when |
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using a network filesystem (such as NFS or CIFS/SMB/Samba.) |
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Unfortunately at this moment the kernel is not caching the response. |
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using a network filesystem (such as NFS or SMB.) Unfortunately at this |
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moment the kernel is not caching the response. |
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.PP |
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To work around this situation mergerfs offers a few solutions. |
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.IP "1." 3 |
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Antonio SJ Musumeci
10 months ago