`/dev/mapper/data-root` does not exist

[zeroby0]

Section: https://mutschler.dev/linux/pop-os-btrfs-22-04/#mount-the-btrfs-top-level-root-filesystem-with-zstd-compression

For some reason the LVM group is not activated, and /dev/mapper/data-root is not created some times. Mounting the btrfs partition throws the error: /dev/mapper/data-root does not exist

ls /dev/mapper
# control cryptdata

sudo lvs
#  LV   VG   Attr       LSize  Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert
#  root data -wi------- 47.39g

Note the missing a flag under Attrs. It indicates the lvm hasn't been activated.

When that happens, run as root:

vgscan --mknodes -v
vgchange -a y data

(credit: https://unix.stackexchange.com/a/24818)

This activates the subvolume. Check again with lvs:

ls /dev/mapper
# control cryptdata data-root

sudo lvs
#  LV   VG   Attr       LSize  Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert
#  root data -wi-a----- 47.39g

Just creating this for people might encounter the same problem. Willi, would you consider adding this to the guide as a side note?