The filesystem options declared for the root file system are apparently ignored. This happens for a btrfs root filesystem on a LUKS volume.
Exerpt from '/etc/config.scm": --8<---------------cut here---------------start------------->8--- (mapped-devices (list (mapped-device (source (uuid "ee90b2aa-97e8-4ae5-ac72-9bf9058cc949")) (target "cryptroot") (type luks-device-mapping)) (mapped-device (source (uuid "ec9cd327-0370-4e20-baa4-254d03b1901e")) (target "cryptguillaume") (type luks-device-mapping)))) (file-systems (cons* (file-system (mount-point "/") (device "/dev/mapper/cryptroot") (type "btrfs") (options "autodefrag,compress=lzo") (dependencies mapped-devices)) (file-system (mount-point "/home/guillaume") (device "/dev/mapper/cryptguillaume") (type "btrfs") (options "autodefrag,compress=lzo") (dependencies mapped-devices)) %base-file-systems)) --8<---------------cut here---------------end--------------->8--- Exerpt from '/etc/fstab': --8<---------------cut here---------------start------------->8--- /dev/mapper/cryptroot / btrfs autodefrag,compress=lzo /dev/mapper/cryptguillaume /home/guillaume btrfs autodefrag,compress=lzo --8<---------------cut here---------------end--------------->8--- Exerpt from '/etc/mtab': --8<---------------cut here---------------start------------->8--- /dev/mapper/cryptroot / btrfs rw,relatime,ssd,space_cache,subvolid=5,subvol=/ 0 0 /dev/mapper/cryptguillaume /home/guillaume btrfs rw,relatime,compress=lzo,ssd,space_cache,autodefrag,subvolid=5,subvol=/ 0 0 /dev/mapper/cryptroot /gnu/store btrfs ro,relatime,ssd,space_cache,subvolid=5,subvol=/gnu/store 0 0 --8<---------------cut here---------------end--------------->8--- Here we see that the options 'autodefrag' and 'compress=lzo' have disappeared on the root filesystem. Maybe it has something to do with the new '/gnu/store' subvolume that appeared?