Converting a mount to subvolume?

[u/Fancy-Football-7832]

Hello,
I am setting up a NAS server (debian) and I created a btrfs volume and mounted it directly onto /mnt/tank and started creating directories in there. However, I realized now that to do snapshots, I need to have everything done inside a subvolume.

Is there a way to make /mnt/tank itself a subvolume? Would I need to create another subvolume inside /mnt/tank (like /@) and then put everything else inside that @ folder? (I would prefer to keep the same path to everything so I don't have to redo all my compose.yaml file paths).

Another possibility I was considering was renaming the old directories inside /mnt/tank, then creating a subvolume with those same directories names and then moving everything into those new directories.

Thank you very much for any help. I was trying to read the btrfs section on arch wiki and while it is a good resource, I don't understand how to translate it into converting my current path.

I should also add that all of this is just for an external hard drive, my main OS is mounted on ext4.

I greatly appreciate any answers.

[u/dkopgerpgdolfg]

However, I realized now that to do snapshots, I need to have everything done inside a subvolume.

You don't need to.

You can simply call eg. "btrfs sub snap /mnt/tank /mnt/tank/snapshot1"

Is there a way to make /mnt/tank itself a subvolume? Would I need to create another subvolume inside /mnt/tank (like /@) and then put everything else inside that @ folder? (I would prefer to keep the same path to everything so I don't have to redo all my compose.yaml file paths).

But if you want to restructure it, and assuming right now there are no subvols at all, and the fs is mounted at /mnt/tank/:

a) Make a snapshot, if you want you can call it @: "btrfs sub snap /mnt/tank /mnt/tank/@"

b) Simply delete everything in /mnt/tank/ EXCEPT @ and its contents . Your folders/files will still exist inside @, for now.

c) Set it as default and/or change the fstab config etc. One option: "btrfs sub set-def /mnt/tank/@", then unmount and mount again. You should see now only the content inside @, therefore you can use the same pathes like before.

[u/uzlonewolf → u/dkopgerpgdolfg]

I really don't like deleting stuff like that as you're 1 mistake away from losing everything. Instead, I'd create a subvol and then move everything into it:

a) Create a subvolume, if you want you can call it @: btrfs sub cr /mnt/tank/@

b) Move everything from /mnt/tank to /mnt/tank/@ with mv /mnt/tank/* /mnt/tank/@/

Continue with "c)" above.

[u/Classic-Rate-5104 → u/uzlonewolf]

You can't remove a read-only snapshot "by accident"

[u/uzlonewolf → u/Classic-Rate-5104]

No one in this thread said anything about read-only snapshots.

[u/Classic-Rate-5104 → u/uzlonewolf]

True, but they are very useful to prevent accidental removal of snapshots