AW: Why subvolumes?

["Andreas Buschka" <a.buschka@tarent.de>]

Hi Jerome,

essentially, a btrfs sub volume is the root of a btrfs (you can take it and mount it as it is). This is critical for the snapshot functionality: If you have a sub volume (consisting of a snapshot) for, say, "/", and your system goes south (e.g. after updating the kernel or another crucial system package), then all you have to do it tell the Linux kernel at the bootloader prompt (via the rootflags=...  parameter)  not to mount the default btrfs, but the snapshot. Then, you can boot the "last known good" state of the system normally and recover from the comfort of a running system.

The main point here is that the default btrfs "sub volume" (which you would normally mount as /) is technically not different from any other sub volume at all.

Best regards,
Andreas

-----Ursprüngliche Nachricht-----
Von: linux-btrfs-owner@vger.kernel.org [mailto:linux-btrfs-owner@vger.kernel.org] Im Auftrag von Jerome Haltom
Gesendet: Dienstag, 23. Juli 2013 14:00
An: Linux Btrfs
Betreff: Q: Why subvolumes?

May I ask why the decision to implement snapshotting through subvolumes? I've been very curious about why the design wasn't to simply allow snapshotting of any directory or file.
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