MergerFS

This is a good option if you just want to combine disks and unlike most other RAID technologies, if you loose a disk the rest will keep going. Many people combine this with SnapRAID for off-line parity.

Prepare and Exempt Disks

Prepare and exempt the file systems from auto-mounting1 so you can supply your own mount options and make sure they are up before you start MergerFS.

Make sure to wipe the disks before using as wipefs and fdisk are not available in LibreELEC.

# Assuming the disks are wiped, format and label each disk the same
mkfs.ext4 /dev/sda 
e2label /dev/sda pool-member

# Copy the udev rule for editing 
cp /usr/lib/udev/rules.d/95-udevil-mount.rules /storage/.config/udev.rules.d
vi /storage/.config/udev.rules.d/95-udevil-mount.rules

Edit this section by adding the pool-member label from above

# check for special partitions we dont want mount
IMPORT{builtin}="blkid"
ENV{ID_FS_LABEL}=="EFI|BOOT|Recovery|RECOVERY|SETTINGS|boot|root0|share0|pool-member", GOTO="exit"

Test this by rebooting and making sure the drives are not mounted.

Add Systemd Mount Units

Each filesystem requires a mount unit like below. Create one for each drive named disk1, disk2, etc. Note: The name of the file is import and to mount /storage/disk1 the name of the file must be storage-disk1.mount

vi /storage/.config/system.d/storage-disk1.mount
[Unit]
Description=Mount sda
Requires=dev-sda.device
After=dev-sda.device

[Mount]
What=/dev/sda
Where=/storage/disk1
Type=ext4
Options=rw,noatime,nofail

[Install]
WantedBy=multi-user.target
systemctl enable --now storage-disk1.mount

Download and Test MergerFS

MergerFS isn’t available as an add-on, but you can get it directly from the developer. LibreELEC (or CoreELEC) on ARM have a 32 bit[^2] user space so you’ll need the armhf version.

wget https://github.com/trapexit/mergerfs/releases/latest/download/mergerfs-static-linux_armhf.tar.gz

tar --extract --file=./mergerfs-static-linux_armhf.tar.gz --strip-components=3 usr/local/bin/mergerfs

mkdir bin
mv mergerfs bin/

Mount the drives and run a test like below. Notice the escaped *. That’s needed at the command line to prevent shell globbing.

mkdir /storage/pool
/storage/bin/mergerfs /storage/disk\* /storage/pool/

Create the MergerFS Service

vi /storage/.config/system.d/mergerfs.service
[Unit]
Description = MergerFS Service
After=storage-disk1.mount storage-disk2.mount storage-disk3.mount storage-disk4.mount
Requires=storage-disk1.mount storage-disk2.mount storage-disk3.mount storage-disk4.mount

[Service]
Type=forking
ExecStart=/storage/bin/mergerfs -o category.create=mfs,noatime /storage/disk* /storage/pool/
ExecStop=umount /storage/pool

[Install]
WantedBy=default.target
systemctl enable --now mergerfs.service

Your content should now be available in /storage/pool after boot.


Last modified March 13, 2024: Added libreelec notes (1b82161)