Does the Arch Linux image already support BTRFS or would I need to compile it into the kernel myself?
If the latter is the case, a short guide on how one would do that would be great.
Yes, it is supported. You have to install the
btrfs-progs package to get user space utilities, but the FS support is built into the kernel by default.
It should be noted that this filesystem is still marked as experimental and therefore, should not be used to store important data.
This is what
mkfs.btrfs says on my Pi:
WARNING! - Btrfs Btrfs v0.19 IS EXPERIMENTAL WARNING! - see http://btrfs.wiki.kernel.org before using