Re: [gentoo-user] planned btrfs conversion: questions

[Marc Joliet]

Am Wed, 07 May 2014 06:56:12 +0800
schrieb William Kenworthy <billk@×××××××××.au>:

> On 05/06/14 18:18, Marc Joliet wrote:
> > Hi all,
> >
> > I've become increasingly motivated to convert to btrfs.  From what I've seen,
> > it has become increasingly stable; enough so that it is apparently supposed to
> > become the default FS on OpenSuse in 13.2.
> >
> > I am motivated by various reasons:
> ....
>
> My btrfs experience:
>
> I have been using btrfs seriously (vs testing) for a while now with
> mixed results but the latest kernel/tools seem to be holding up quite well.
>
> ~ 2yrs on a Apple/gentoo laptop (I handed it back to work a few months
> back) - never a problem! (mounted with discard/trim)

That's one HDD, right? From what I've read, that's the most tested and stable
use case for btrfs, so it doesn't surprise me that much that it worked so well.

> btrfs on a 128MB intel ssd (linux root drive) had to secure reset a few
> times as btrfs said the filesystem was full, but there was 60G+ free -
> happens after multiple crashes and it seemed the btrfs metadata and the
> ssd disagreed on what was actually in use - reset drive and restore from
> backups :(  Now running ext4 on that drive with no problems - will move
> back to btrfs at some point.

All the more reason to stick with EXT4 on the SSD for now.

[snip interesting but irrelevant ceph scenario]
>
> 3 x raid 0+1 (btrfs raid 1 with 3 drives) - working well for about a month

That last one is particularly good to know. I expect RAID 0, 1 and 10 to work
fairly well, since those are the oldest supported RAID levels. 

> ~10+ gentoo VM's, one ubuntu and 3 x Win VM's with kvm/qemu storage on
> btrfs - regular scrubs show an occasional VM problem after system crash
> (VM server), otherwise problem free since moving to pure btrfs from
> ceph.  Gentoo VM's were btrfs in raw qemu containers and are now
> converted to qcow2 - no problems since moving from ceph.  Fragmentation
> on VM's is a problem but "cp --reflink vm1 vm2" for vm's is really
> really cool!

That matches the scenario from the ars technica article; the author is a huge
fan of file cloning in btrfs :) .

And yeah, too bad autodefrag is not yet stable.

> I have a clear impression that btrfs has been incrementally improving
> and the current kernel and recovery tools are quite good but its still
> possible to end up with an unrecoverable partition (in the sense that
> you might be able to get to some of the the data using recovery tools,
> but the btrfs mount itself is toast)
>
> Backups using dirvish - was getting an occasional corruption (mainly
> checksum) that seemed to coincide with network problems during a backup
> sequence - have not seen it for a couple of months now.  Only lost whole
> partition once :(  Dirvish really hammers a file system and ext4 usually
> dies very quickly so even now btrfs is far better here.

I use rsnapshot here with an external hard drive formatted to EXT4. I'm not
*that* worried about the FS dying, more that it dies at an inopportune moment
where I can't immediately restore it.

[again, snip interesting but irrelevant ceph scenario]
>
> I am slowly moving my systems from reiserfs to btrfs as my confidence in
> it and its tools builds.  I really dislike ext4 and its ability to lose
> valuable data (though that has improved dramaticaly) but it still seems
> better than btrfs on solid state and hard use - but after getting burnt
> I am avoiding that scenario so need to retest.

Rising confidence: good to hear :) .

Perhaps this will turn out similarly to when I was using the xf86-video-ati
release candidates and bleeding edge gentoo-sources/mesa/libdrm/etc. (for 3D
support in the r600 driver): I start using it shortly before it starts truly
stabilising :) .

-- 
Marc Joliet
--
"People who think they know everything really annoy those of us who know we
don't" - Bjarne Stroustrup