AW: WG: How to properly setup for snapshots

From: Claudius Ellsel <claudius.ellsel@live.de>
To: Andrei Borzenkov <arvidjaar@gmail.com>,
	Roman Mamedov <rm@romanrm.net>, Remi Gauvin <remi@georgianit.com>
Cc: linux-btrfs <linux-btrfs@vger.kernel.org>
Subject: AW: WG: How to properly setup for snapshots
Date: Mon, 21 Dec 2020 18:35:57 +0000	[thread overview]
Message-ID: <AM9P191MB1650526777331A5E93DAADD3E2C00@AM9P191MB1650.EURP191.PROD.OUTLOOK.COM> (raw)
In-Reply-To: <3d45b062-a004-277e-db8b-6826c6b342bb@gmail.com>

I was aware that snapshots are basically subvolumes. Currently I am looking for an easy way to achieve what I want. I currently just want to be able to create manual snapshots and an easy way to restore stuff on file level. For that (including the management of snapshots), snapper seems to be the best way, as btrfs does not offer such features (in an easy way) out of the box afaict.

Unfortunately the documentation for snapper is also not nice, I just had a closer look again. The best I could find was the Arch wiki but that also starts right away with how to create a config (without telling whether that is even needed for basic usage).

Ultimately I'd like to have a btrfs Wiki entry for snapshots and am willing to help with it.

Von: Andrei Borzenkov <arvidjaar@gmail.com>
Gesendet: Montag, 21. Dezember 2020 19:26
An: Roman Mamedov <rm@romanrm.net>; Remi Gauvin <remi@georgianit.com>
Cc: Claudius Ellsel <claudius.ellsel@live.de>; linux-btrfs <linux-btrfs@vger.kernel.org>
Betreff: Re: WG: How to properly setup for snapshots 

21.12.2020 20:37, Roman Mamedov пишет:
> On Mon, 21 Dec 2020 12:05:37 -0500
> Remi Gauvin <remi@georgianit.com> wrote:
> 
>> I suggest making a new Read/Write subvolume to put your snapshots into
>>
>> btrfs subvolume create .my_snapshots
>> btrfs subvolume snapshot -r /mnt_point /mnt_point/.my_snapshots/snapshot1
> 
> It sounds like this could plant a misconception right from the get go.
> 
> You don't really put snapshot* "into" a subvolume. Subvolumes do not actually
> contain other subvolumes, since making a snapshot of the "parent" won't
> include any content of the subvolumes with pathnames below it.
> 
> As such there's no benefit in storing snapshots "inside" a subvolume. There's

Having dedicated subvolume containing snapshots makes it easy to switch
your root between subvolumes (either for roll back or transactional
updates or whatever) and retain access to snapshots by simply mounting
containing subvolume. Having them in subdirectory of your (root)
subvolume means you can no more remove this subvolume without also
destroying snapshots before, so you are stuck with it.

So it makes all sort of sense to think in advance and prepare dedicated
subvolume for this purpose.

> not much of the "inside". Might as well just create a regular directory for
> that -- and with less potential for confusion.
> 
> * - keep in mind that "snapshot" and "subvolume" mean the same thing in Btrfs,
>     the only difference being that "snapshot"-subvolume started its life as
>     being a full copy(-on-write) of some other subvolume.
> 