subvols and parents - how?

[Christoph Anton Mitterer <calestyo@scientia.net>]

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Hey.

I'd have a, mainly administrative, question.

When I use subvolumes than these have always a parent subvolume (except
ID5), so I can basically decide between two ways:

a) make child subvolumes, e.g.
5
|
+-root   (=subvol, mountpoint /)
  +-boot/
  +-root/
  +-lib/
  +-home/ (=subvolume)
and soon on... perhaps the whole thing without the dedicated root-
subovlume (although that's probably not so smart, I guess).

b) place at least some of the subvolumes directly below the top-level
and mount them e.g. via /etc/fstab, e.g.
5
|
+-root   (=subvol, mountpoint /)
| +-boot/
| +-root/
| +-lib/
+-home/ (=subvolume, mountpoint /home)


Now I wondered whether this has any technical implications, but neither
the wiki, nor the manpages seem to explain a lot here.


The "differences", AFAIU, are the follows:
- When I mount a given subvolume,.. it's childs are automatically 
  "there".
  Whereas when I don't have them as childs (as in (b)) I must of
  course mount them somehow manually.
- Analogously for umounting.
- I can move existing subvols to higher/lower levels, and the parent
  IDs will change accordingly.

So basically it makes no difference, right? Or is there anything more
technical going on? E.g. with the ref-links or so?
Right now, there are, AFAIK, neither recursive snapshots (and
especially not atomic ones) nor recursive send/receive, right?
If that should ever be implemented, would I perhaps have problems with 
(a) or (b)?


Thanks,
Chris.

btw, for a developer:
$ btrfs subvolume list /mnt/ -pacguqt
ID      gen     cgen    parent  top level       parent_uuid     uuid    path    
--      ---     ----    ------  ---------       -----------     ----    ----    
257     16      8       5       5               -       64f8a75b-5cb5-6e4d-9f30-d45fe3d9e060    <FS_TREE>/root

There seem to be some colum mis-aglinment issues in the output =)
btrfsprogs 4.3

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