Arch Linux

Pafrapé

Member

Registered: 2010-10-25

Posts: 48

systemd-homed : btrfs or ext4 ?

Hello.
I'm about to perform a fresh installation of Arch Linux.
I'll be using two NVMe drives: one for the system and one for `/home`.
I plan to set up systemd-homed on /home.

A quick question: What is the best type of formatting for the hard drive that will host /home and systemd-homed? Btrfs or ext4?

Thanks for the advice.

Last edited by Pafrapé (2026-09-29 07:30:45)

topcat01

Member

Registered: 2019-09-17

Posts: 345

Re: systemd-homed : btrfs or ext4 ?

btrfs should be fine for homed images. I have been switching to btrfs myself because apart from the snapshot and data integrity features, btrfs is great at diagnosing and reporting failing/misbehaving hardware early, before data is lost. The usual caveats apply: do not let "unallocated space" drop too low, and do not use raid5/6.

Pafrapé

Member

Registered: 2010-10-25

Posts: 48

Re: systemd-homed : btrfs or ext4 ?

After research, I think the best way to format my hard drive—which will only contain `/home` and on which I will install `systemd-homed`—is ext4.
Indeed, homed natively uses Btrfs.
Formatting `/home` with Btrfs while `systemd-homed` natively uses Btrfs puts a double load on the CPU and causes instability by performing Copy-on-Write twice simultaneously.
Furthermore, snapshots are not possible with `systemd-homed`.
In conclusion, the ideal setup is to install homed, natively formatted in Btrfs, on a storage medium formatted in ext4.

topcat01

Member

Registered: 2019-09-17

Posts: 345

Re: systemd-homed : btrfs or ext4 ?

Yes, there are a few options. I prefer

homectl create --storage=luks --fs-type=ext4 ...

to keep things simple inside the LUKS container, and keep the loopback file on btrfs, so I can snapshot and back up the containing subvolume (send/receive).

This is the opposite of my approach to (Linux) VM images, where I use ext4 for storing the image, and btrfs inside the VM, since the VM offers full flexibility w.r.t. the filesystem.

Last edited by topcat01 (2026-09-29 17:57:38)

Pafrapé

Member

Registered: 2010-10-25

Posts: 48

Re: systemd-homed : btrfs or ext4 ?

Actually, you did the opposite of me:
- /home formatted as btrfs
- homed formatted as ext4.
Is that right?

What are the benefits?

topcat01

Member

Registered: 2019-09-17

Posts: 345

Re: systemd-homed : btrfs or ext4 ?

Yes exactly . Of course, I want to avoid btrfs on btrfs, and doing it this way gives me slightly more flexibility in incrementally backing up the homed image, while still preserving data integrity. Backups can happen even if the homed user is not logged on. Also, the /home partition has a few regular users, so I want to protect the entire /home fs using btrfs.

The disadvantage is that btrfs does not see the individual files in the homed image, so if there is data corruption then scrub won't tell me which file was affected. Once the inner btrfs is mounted (in your case), you can still ro snapshot and send those. So you don't lose too much there.