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

["Stefan G. Weichinger" <lists@xunil.at>]

Am 12.05.2014 16:30, schrieb Marc Joliet:

> 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.

Yes. I will maybe look into your link sometimes ...

What I want to research:

systemd is now able to "detect" / and /home (and swap) via the GPT-IDs
... I wonder if I could get rid of fstab or at least the entries for /

Right now when I test my rollbacks I edit (a) the subvolid in the
kernel-line of grub.cfg and (b) in /etc/fstab on the "target" subvol.

Maybe the second part is redundant, I don't know?

I think of generating something like a daily "last known good rootfs"
and a related entry in grub2 :-)

Just playing here so far, but interesting options.

(2nd thought: the subvol would then need to get that GPT-ID?)

>> 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).

So far I run one btrfs on a partition (/dev/sdc3) of an SSD (containing
my active /, /home and some data I want to have mounted with speedy
performance) and a second btrfs on a 1TB-HDD.

I decided to degrade my mdadm RAID1 and dedicate one of the hdds (sdd)
completely to btrfs ... then migrated the old LVs into subvols today.

Looking good so far (right now I have no more active LVs here ...).

Next steps:

* see if things work :-)

* migrate my other, faster and bigger SSD to the new and shiny root-fs.
I boot from the EFI partition there ... but root and stuff is on the 2nd
SSD.

* decide if to get rid of the old Win7-partition (on sdb) that wasn't
booted for years (?) now ... if I don't do that I don't have a second
hdd with the same size for mirroring the btrfs ...

a) sdd = sdb

b) size of sdd > (size of sdb minus partition-win7)

So more to consider here.

But the btrfs contains mostly pics and music and test-vms ... all backed
up via amanda to tape nearly daily, so no specific need for mirroring.


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

Thanks for the reminder .. it fits into my cleaning up here ;-)

Now for some scrubbing, backups and watching TV in the meantime.

Greets, Stefan