[systemd-devel] systemd and nested Btrfs subvolumes

Lennart Poettering mzerqung at 0pointer.de
Sun Mar 22 21:50:41 PDT 2015

On Thu, 19.03.15 19:27, Chris Murphy (lists at colorremedies.com) wrote:

> Short version:
> ------------------
>   Instead of machinectl clone using btrfs snapshots, or even needing
> to store things in a var/lib/machines Btrfs subvolume, does it meet
> the requirements for Btrfs optimization to do this with cp -a
> --reflink instead?

No. That is neither atomic nor efficient (since it requires opening
every single file in the tree), not particularly discoverable: I think
it's a good idea that users can enumerate subvolumes.

> Why? Nested subvolumes are confusing. And nested subvolumes are
> excluded from snapshots. Subvolume B inside of Subvolume A, will not
> be snapshot or rolled back, if I snapshot Subvolume A and subsequently
> rollback to the snapshot of A. Is this the intended workflow?

I am pretty sure the right answer to this problem to get recursive
snapshotting and subvolume deletion into place, so that the issues go

The right place to fix this in the kernel, but I figure in the worst
case this could even be emulated in userspace...


Lennart Poettering, Red Hat

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