Using MergerFS to combine multiple hard drives into one unified media storage

March 11, 2024

updated

March 16, 2024

My situation was simple -- I have on my home server a 2 TB hard drive for media storage that was filling up, and I wanted to add a second drive, but not have to keep track of which drive specific files were in. Enter mergerfs, an open source "union filesystem" that lets you merge multiple storage drives into one mount point.

What and Why

MergerFS is free and open source software described as a “featureful union filesystem.” I discovered it (along with easy to understand set up instructions) via Perfect Media Server, itself a great resource for self-hosters. Essentially what MergerFS does is act as a proxy so that multiple hard drives can be accessed at one mount point. What does that mean? Well, lets go over my situation.

I had a 2 TB hard drive where I kept only video files at /dev/sdb, and another 1 TB drive with my music and photos at /dev/sdc. I wanted to add a third drive that already had some other movies and lots of free space at /dev/sdd. The folder structure looked like this:

/dev/sdb
  ├── movies
  └── tvshows
/dev/sdc
  ├── music
  └── photos
/dev/sdd
  └── movies

But how to keep track of what files are in which hard drive? How to just not worry about where they end up? MergerFS that’s how. It will unify all three drives into one mount point where you can access everything. The file structure will be like this:

/media
  ├── movies
  ├── music
  ├── photos
  └── tvshows

I like to put all my stuff in my home directory (/home/ad/...) so I had each drive mounted there and will still mount the new unified storage in there at /home/ad/media. You don’t have to do this and it may not even be best practice, but I’m set in my ways and I’m the only one that accesses this server. Feel free to use a different unified mount point like /opt/media or /srv/media.

With their powers combined, I gain access any media across all three drives at my chosen single mount point, which live in my home directory at /home/ad/media, where it’s all accessible by Plex and other services.

Install and configure MergerFS

MergerFS can be installed via sudo install mergerfs, but the stable release on your distro’s repositories may not have the most up-to-date available. I’ll be using the latest release from the GitHub page as recommended. (Make sure you get the correct version for the system you’re running, the examples below use the version specific to my distro and architecture.)

First download it:

wget https://github.com/trapexit/mergerfs/releases/download/2.40.2/mergerfs_2.40.2.debian-bookworm_amd64.deb

Then install it:

dpkg -i mergerfs_2.40.2.debian-bookworm_amd64.deb

Configuration is simple, done just by editing /etc/fstab. First, an example of how my fstab file looked before MergerFS, when I was mounting each HDD into a subdirectory within my home directory.

...
UUID=218236ca-8e14-47ae-866a-a91e70c88a2a   /home/ad/videos       ext4    errors=remount-ro   0   0
UUID=5e3d1d44-2979-488d-a21a-9fa06508c470   /home/ad/other   ext4    errors=remount-ro   0   0
UUID=cce7cdab-a2df-4d4f-aac3-98fab2afdbd5   /home/ad/extra    ext4    errors=remount-ro   0   0

As suggested by Perfect Media Server, I changed the mount points for each drive to be /mnt/media1, /mnt/media2, and /mnt/media3. (Which is which does not really mattter anymore.) This way by using /mnt/media* for the new mergerfs entry in fstab, it will pick up all the drives and any future ones I add that uses the same scheme. The new unified single mount point will be in /home/ad/media, still in my home directory like I had it before, but now everything in one directory instead of multiple ones.

Here’s how my fstab file looks now.

...
UUID=218236ca-8e14-47ae-866a-a91e70c88a2a   /mnt/media1   ext4    errors=remount-ro   0   0
UUID=5e3d1d44-2979-488d-a21a-9fa06508c470   /mnt/media2   ext4    errors=remount-ro   0   0
UUID=cce7cdab-a2df-4d4f-aac3-98fab2afdbd5   /mnt/media3   ext4    errors=remount-ro   0   0
/mnt/media*   /home/ad/media    fuse.mergerfs   defaults,allow_other,use_ino,cache.files=off,moveonenospc=true,dropcacheonclose=true,category.create=mfs,fsname=mergerfs    0   0

I used the options suggested at Perfect Media Server and have had no issues, but feel free to read up on all the available options use different ones.

Once the changes were made in /etc/fstab, I unmounted all the drives from their old mount points, created the new mount point, and rebooted so the new fstab config would take effect.

cd ~/
sudo umount videos other extra
mkdir media
sudo reboot

Once the machine is back up and I’m reconnected via SSH, it’s time to check if everything shows up where it’s supposed to.

ls ~/media
movies  music  photos  tvshows

Exploring your new unified mount point should show all your data! At that point you can delete the old mounts points if you haven’t already and point your services at the new unified mount point.

If you encounter a problem after reboot, you probably messed something up in the fstab file, the syntax can be tricky. Edit it to fix any issues and reboot again. If you want to be safe, try commenting out rather than editing any existing fstab entries until you know everything is working properly.