I have a btrfs subvolume structure that allows me easy snapshotting of targetted folders, but it appears that one of my btrfs subvolumes is not getting mounted at all. This is weird, considering other nested subvolumes (i.e. @git within @opt) work without problems.
$ btrfs subvolume list /
ID 256 gen 7946 top level 5 path @rootfs
ID 260 gen 6537 top level 5 path @snapshots
ID 261 gen 4407 top level 5 path @swap
ID 262 gen 7934 top level 5 path @root
ID 263 gen 7939 top level 5 path @home
ID 264 gen 7946 top level 5 path @tmp
ID 265 gen 6542 top level 5 path @pkg
ID 266 gen 7946 top level 5 path @log
ID 267 gen 7937 top level 5 path @etc
ID 268 gen 7472 top level 5 path @opt
ID 269 gen 7475 top level 5 path @www
ID 270 gen 7473 top level 5 path @git
ID 271 gen 7492 top level 5 path @minecraft
ID 272 gen 7491 top level 5 path @minecraft-dynmap
ID 273 gen 7460 top level 5 path @factorio
ID 274 gen 7464 top level 5 path @openttd
$ cat /etc/fstab
/dev/mapper/vg1-lv1 / btrfs defaults,subvol=@rootfs 0 0
/dev/mapper/vg1-lv1 /.snapshots btrfs defaults,subvol=@snapshots 0 0
/dev/mapper/vg1-lv1 /.swap btrfs subvol=@swap 0 0
# /.swap/swap.img none swap sw 0 0
/dev/mapper/vg1-lv1 /root btrfs defaults,subvol=@root 0 0
/dev/mapper/vg1-lv1 /home btrfs defaults,subvol=@home 0 0
/dev/mapper/vg1-lv1 /tmp btrfs defaults,subvol=@tmp 0 0
/dev/mapper/vg1-lv1 /var/cache/apt btrfs defaults,subvol=@pkg 0 0
/dev/mapper/vg1-lv1 /var/log btrfs defaults,subvol=@log 0 0
/dev/mapper/vg1-lv1 /etc btrfs defaults,subvol=@etc 0 0
/dev/mapper/vg1-lv1 /opt btrfs defaults,subvol=@opt 0 0
/dev/mapper/vg1-lv1 /var/www btrfs defaults,subvol=@www 0 0
/dev/mapper/vg1-lv1 /opt/git btrfs defaults,subvol=@git 0 0
/dev/mapper/vg1-lv1 /opt/factorio btrfs defaults,subvol=@factorio 0 0
/dev/mapper/vg1-lv1 /opt/minecraft btrfs defaults,subvol=@minecraft 0 0
/dev/mapper/vg1-lv1 /opt/minecraft/plugins/dynmap btrfs defaults,subvol=@minecraft-dynmap 0 0
/dev/mapper/vg1-lv1 /opt/openttd btrfs defaults,subvol=@openttd 0 0
$ cat /proc/mounts | grep subvol=
/dev/mapper/vg1-lv1 / btrfs rw,relatime,ssd,space_cache,subvolid=256,subvol=/@rootfs 0 0
/dev/mapper/vg1-lv1 /.snapshots btrfs rw,relatime,ssd,space_cache,subvolid=260,subvol=/@snapshots 0 0
/dev/mapper/vg1-lv1 /.swap btrfs rw,relatime,ssd,space_cache,subvolid=261,subvol=/@swap 0 0
/dev/mapper/vg1-lv1 /home btrfs rw,relatime,ssd,space_cache,subvolid=263,subvol=/@home 0 0
/dev/mapper/vg1-lv1 /etc btrfs rw,relatime,ssd,space_cache,subvolid=267,subvol=/@etc 0 0
/dev/mapper/vg1-lv1 /opt btrfs rw,relatime,ssd,space_cache,subvolid=268,subvol=/@opt 0 0
/dev/mapper/vg1-lv1 /tmp btrfs rw,relatime,ssd,space_cache,subvolid=264,subvol=/@tmp 0 0
/dev/mapper/vg1-lv1 /root btrfs rw,relatime,ssd,space_cache,subvolid=262,subvol=/@root 0 0
/dev/mapper/vg1-lv1 /var/cache/apt btrfs rw,relatime,ssd,space_cache,subvolid=265,subvol=/@pkg 0 0
/dev/mapper/vg1-lv1 /var/log btrfs rw,relatime,ssd,space_cache,subvolid=266,subvol=/@log 0 0
/dev/mapper/vg1-lv1 /var/www btrfs rw,relatime,ssd,space_cache,subvolid=269,subvol=/@www 0 0
/dev/mapper/vg1-lv1 /opt/factorio btrfs rw,relatime,ssd,space_cache,subvolid=273,subvol=/@factorio 0 0
/dev/mapper/vg1-lv1 /opt/git btrfs rw,relatime,ssd,space_cache,subvolid=270,subvol=/@git 0 0
/dev/mapper/vg1-lv1 /opt/minecraft btrfs rw,relatime,ssd,space_cache,subvolid=271,subvol=/@minecraft 0 0
/dev/mapper/vg1-lv1 /opt/openttd btrfs rw,relatime,ssd,space_cache,subvolid=274,subvol=/@openttd 0 0
$ journalctl -xb | grep minecraft
Aug 22 17:06:36 primary systemd[1]: Mounting /opt/minecraft...
░░ Subject: A start job for unit opt-minecraft.mount has begun execution
░░ A start job for unit opt-minecraft.mount has begun execution.
Aug 22 17:06:36 primary systemd[1]: Mounted /opt/minecraft.
░░ Subject: A start job for unit opt-minecraft.mount has finished successfully
░░ A start job for unit opt-minecraft.mount has finished successfully.
As you can see, minecraft-dynmap subvolume is not getting mounted, and does not appear in /proc/mounts, unlike other nested subvolumes, which get mounted ok.
Mounting the subvolume with mount -t btrfs -o defaults,subvol=@minecraft-dynmap /dev/mapper/vg1-lv1 /opt/minecraft/plugins/dynmap or mount -a works as expected, although naturally, does not persist across reboots.
Is there a limit to how many subvolumes you can nest within each self? I.e. @rootfs/@opt/@git/ and @rootfs/@opt/@minecraft/ works, but @rootfs/@opt/@minecraft/@minecraft-dynmap breaks?
I have scoured dmesg and journalctl -xb / journalctl -xe but found no entry that would explain this behaviour.
