The master branch for cp now defaults to copy-on-write on filesystems
that support reflinks, which should make copies more efficient if
Fedora starts using btrfs:
Dolphin and KIO also seem like they will start doing this:
Beyond these recent changes, there are many other reasons to use
btrfs, such as that Podman has a btrfs driver that might make
containers more efficient, that ostree makes limited use of reflinks
when they are available, that many filesystem options can be changed
and new features and better defaults used even after the filesystem
was initially created, that resize operations can be done online, and
that there are uniform checksums on all metadata blocks, giving
guarantees against corruption.
XFS also has reflinks, but lacks many features of btrfs, and switching
from ext4 to XFS would mean losing cgroup writeback. XFS would mean
no transparent compression too.
Switching from ext4 to OpenZFS, even putting aside license concerns
from Red Hat, risks kernel releases being delayed or Fedora not being
able to release with recent kernels. It makes kernel updates in Fedora
dependent on the OpenZFS community releasing new versions compatible
with recent kernels fast enough. And this is a concern, because many
upstream kernel maintainers indicated they have little interest
in avoiding breaking OpenZFS or doing any extra work to get it to
work. (See, notably, https://lkml.org/lkml/2019/1/10/733
I appreciate that Fedora’s kernel maintainers release new kernels
quickly and think this is something that works well in Fedora.
Supporting any out-of-tree modules in Fedora repos, including
filesystems, would endanger this.
Also, in general, I think it is not a good idea to use things that
your upstreams are not interested in, do not want to support, and do
not recommend using.
Staying on ext4 means not having reflinks, transparent compression,
online resize, deduplication, strong guarantees against corruption,
and that improved filesystem defaults or new features can be used only
by recreating the filesystem and reinstalling Fedora. In consideration
of that, I am favorable to the change proposal targeting btrfs