Re: [gentoo-user] btrfs conversion: first impressions

[Marc Joliet]

Am Sun, 11 May 2014 23:24:34 +0200
schrieb "Stefan G. Weichinger" <lists@×××××.at>:

[...]
> ... but it is really nice-to-have the option to snapshot your root-fs,
> do-something-to-it (emerge unstable stuff, delete the wrong files, you
> name it ...), and if you don't like it you simply boot using your
> snapshot ... that is actually really helpful and also rather easy once
> you get your head wrapped around the concepts and the few steps
> necessary (and it's quick: the snapshot is done in a blink ...)

In a presentation by Donny Berkholz at Fosdem this year [0], he mentioned the
distro CoreOS, and that they can do atomic updates. I haven't looked it up in
detail, but they're website says that they use a dual-root scheme where the
update is performed in a second root, which is made the real root after
rebooting or after a kexec [1]. It seems to me that this could be made simpler
and easier with btrfs snapshots.

> As far as I researched btrfs seems to be quite reliable in a not too
> complex (read: multi devices) setup ... and backups never hurt anyway.

Of course, for me one of *the* big features was the capability to automatically
fix corrupted data (the self-healing features of btrfs). This is only possible
when you have redundancy across multiple devices. (I'm running a scrub right
now.)

But even with a single device, you can at least *detect* corruption, I just
want to also be able to have it automatically *corrected*.

> As I do backups all the time I feel quite confident to test my setups
> for the next few days and maybe even completely overhaul my desktop setup.

Ditto :) . As risky as it is, this was also a "test" of my backup, in the
sense that, while I knew the backups looked okay by manual inspection, I
hadn't actually restored from backup yet. Obviously, it worked :) .

> -> 2x 1TB HDDs plus 1x 256GB SSD (plus the one older 80GB SSD for tests
> right now) ... with LVM and stuff (remember my hassles last week with
> the LVMs not activated??) ... I could run one btrfs-pool on the 2 HDDs
> and one on the SSD and cut all of my various filesystems out of that.
>
> Would mixing hdds and the ssd into one pool make sense? I think, no ... ?

I suspect something like bcache would work (except I remember reading that
btrfs does not work with it yet).

> --
>
> I will also test running VMs on btrfs-subvolumes and doing snapshots:
>
> snapshot the underlying subvolume, apply some changes within the VM and
> then rollback to the snapshot.
>
> This would remove LVM-snapshotting out of the way ... etc etc
>
> As mentioned before, looking forward ... and curious!

I'm glad I motivated some people to try btrfs themselves :) .

[0] https://www.youtube.com/watch?v=egjcVGKwnrw
[1] http://coreos.com/using-coreos/updates/ (section "technical details")
-- 
Marc Joliet
--
"People who think they know everything really annoy those of us who know we
don't" - Bjarne Stroustrup