Re: WG: How to properly setup for snapshots

[Andrei Borzenkov <arvidjaar@gmail.com>]

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.
>