Btrfs as the default filesystem?

[emanuc]

I decided to open an issue based on this comment: https://github.com/pop-os/distinst/pull/286#issuecomment-1154043654
I hope it will be useful.

It's nice that popOS is planning to change the filesystem to Btrfs by default. I have been using Btrfs for many years with great satisfaction, snapshots are very useful.
I would like to pay attention to some aspects:

• Enable zstd level 1 compression, Fedora has been using it since version 34: https://fedoraproject.org/wiki/Changes/BtrfsTransparentCompression#Summary

If snapshots are enabled by default:

• Exclude unnecessary folders at the time of restore, there are many folders under "/var" that the user may not want to include in snapshots, this has the advantage of having minimal snapshots and taking up little space over time.
  There are issues on Fedora and openSUSE for including package manager database at "/usr/..." to facilitate snapshot management.
  https://fedoraproject.org/wiki/Changes/RelocateRPMToUsr
  http://lists.rpm.org/pipermail/rpm-maint/2017-October/006681.html
  EDIT: To clarify, on openSUSE and from Fedora 36 the rpm database has already been moved to "/usr"

emanu@fedora ~> ls -l /var/lib/rpm
lrwxrwxrwx. 1 root root 26 10 mag 21.05 /var/lib/rpm -> ../../usr/lib/sysimage/rpm/

I understand that it is a non trivial change and it could also depend on your upstream (Ubuntu) so maybe initially creating some additional subvolumes could improve the situation in case of automated snapshots, this is my layout (It allows me to have minimal snapshots):

UUID=1dfbd78c-313d-44a6-9612-2c7b45bed032 /                       btrfs   noatime,compress=zstd:1,subvol=@ 0 0
UUID=4323-EA93          /boot/efi               vfat    umask=0077,shortname=winnt 0 2
UUID=1dfbd78c-313d-44a6-9612-2c7b45bed032 /home                   btrfs   noatime,compress=zstd:1,subvol=@home    0 0
UUID=1dfbd78c-313d-44a6-9612-2c7b45bed032 /var/cache              btrfs   noatime,compress=zstd:1,subvol=var_cache 0 0
UUID=1dfbd78c-313d-44a6-9612-2c7b45bed032 /var/lib/flatpak        btrfs   noatime,compress=zstd:1,subvol=var_lib_flatpak 0 0
UUID=1dfbd78c-313d-44a6-9612-2c7b45bed032 /var/lib/libvirt        btrfs   noatime,compress=zstd:1,subvol=var_lib_libvirt 0 0
UUID=1dfbd78c-313d-44a6-9612-2c7b45bed032 /var/lib/machines       btrfs   noatime,compress=zstd:1,subvol=var_lib_machines 0 0
UUID=1dfbd78c-313d-44a6-9612-2c7b45bed032 /var/log                btrfs   noatime,compress=zstd:1,subvol=var_log 0 0
UUID=1dfbd78c-313d-44a6-9612-2c7b45bed032 /var/tmp                btrfs   noatime,compress=zstd:1,subvol=var_tmp 0 0

Thanks and good job