Gregory's Server
@dside Fair point. However, as far as immutable systems go, does it matter? The job of the filesystem that holds your / (or /usr, if we go by Poettering's suggestion) is to just hold system binaries and other system files that don't need to change save for an update. Does it need some fancy-shmancy FS? I'd say even BTRFS is pretty redundant for this.
@drq yeah, probably not.
I had to look at how OSTree handles this, and all it asks for are hardlinks, although it still claims to benefit from btrfs somehow (I couldn't quickly find how exactly): https://ostreedev.github.io/ostree/introduction/#comparison-with-blockimage-replication
It also mentions git's design a lot, probably with good reason.