mergerfs/mkdocs/docs/quickstart.md

QuickStart

Install

First ensure you have the latest version installed.

Configuration

mergerfs has many options and effectively all of them are functional in nature. What that means is that there is no "best" or "fastest" configuration. No "make faster" options. Everything changes behavior. Sometimes those changes in behavior affect performance.

If you don't already know that you have special requirements then use one of the following option sets as it will cover the common use cases.

You use Linux v6.6 or above

• cache.files=off
• category.create=pfrd
• func.getattr=newest
• dropcacheonclose=false

See Known Issues and Bugs#Software Using mmap for more details why the Linux and mergerfs version matter and its relation to mmap.

NOTE: This "auto mmap" feature is only supported in mergerfs v2.41.0 and above. For older versions see below or the docs from that release.

You use Linux v6.5 or below

You need mmap

To keep the details in a single location: see Known Issues and Bugs#Software Using mmap for more details.

• cache.files=auto-full
• category.create=pfrd
• func.getattr=newest
• dropcacheonclose=true

You don't need mmap

• cache.files=off
• category.create=pfrd
• func.getattr=newest
• dropcacheonclose=false

Usage

For some suggestions on branch setup see the page on branches.

Command Line

mergerfs -o cache.files=off,category.create=pfrd,func.getattr=newest,dropcacheonclose=false /mnt/hdd0:/mnt/hdd1 /media

/etc/fstab

/mnt/hdd0:/mnt/hdd1 /media mergerfs cache.files=off,category.create=pfrd,func.getattr=newest,dropcacheonclose=false 0 0

/etc/fstab w/ config file

For more complex setups it can be useful to separate out the config.

/etc/fstab

/etc/mergerfs/branches/media/* /media mergerfs config=/etc/mergerfs/config/media.ini

/etc/mergerfs/config/media.ini

cache.files=off
category.create=pfrd
func.getattr=newest
dropcacheonclose=false
# comments and empty lines are supported

/etc/mergerfs/branches/media/

Create a bunch of symlinks to point to the branch. mergerfs will resolve the symlinks and use the real path.

ls -lh /etc/mergerfs/branches/media/*

lrwxrwxrwx 1 root root 21 Aug  4  2023 hdd00 -> /mnt/hdd/hdd00
lrwxrwxrwx 1 root root 21 Aug  4  2023 hdd01 -> /mnt/hdd/hdd01
lrwxrwxrwx 1 root root 21 Aug  4  2023 hdd02 -> /mnt/hdd/hdd02
lrwxrwxrwx 1 root root 21 Aug  4  2023 hdd03 -> /mnt/hdd/hdd03

systemd (simple)

/etc/systemd/system/mergerfs-media.service

[Unit]
Description=mergerfs /media service
After=local-fs.target network.target

[Service]
Type=simple
KillMode=none
ExecStart=/usr/bin/mergerfs \
  -f \
  -o cache.files=off \
  -o category.create=pfrd \
  -o func.getattr=newest \
  -o dropcacheonclose=false \
  /mnt/hdd0:/mnt/hdd1 \
  /media
ExecStop=/usr/bin/umount /media
# Or if you need fusermount
# ExecStop=/usr/bin/mergerfs-fusermount -u /media
Restart=on-failure

[Install]
WantedBy=default.target

systemd (w/ setup script)

Since it isn't well documented otherwise: if you wish to do some setup before you mount mergerfs follow this example.

setup-for-mergerfs

/usr/local/bin/setup-for-mergerfs

#!/usr/bin/env sh

# Perform setup
/bin/sleep 10

# Report back to systemd that things are ready
/bin/systemd-notify --ready

setup-for-mergerfs.service

/etc/systemd/system/setup-for-mergerfs.service

[Unit]
Description=mergerfs setup service

[Service]
Type=notify
RemainAfterExit=yes
ExecStart=/usr/local/bin/setup-for-mergerfs

[Install]
WantedBy=default.target

mergerfs-media.service

/etc/systemd/system/mergerfs-media.service

[Unit]
Description=mergerfs /media service
Requires=setup-for-mergerfs.service
After=local-fs.target network.target prepare-for-mergerfs.service

[Service]
Type=simple
KillMode=none
ExecStart=/usr/bin/mergerfs \
  -f \
  -o cache.files=off \
  -o category.create=pfrd \
  -o func.getattr=newest \
  -o dropcacheonclose=false \
  /mnt/hdd0:/mnt/hdd1 \
  /media
ExecStop=/usr/bin/umount /media
# Or if you need fusermount
# ExecStop=/usr/bin/mergerfs-fusermount -u /media
Restart=on-failure

[Install]
WantedBy=default.target