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

[William Kenworthy <billk@iinet.net.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)

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.

cephfs - rolling disaster but its more to do with not giving the system
adequate resources and using what from ceph's point of view are bad
practises (running ceph on the same machine used for VM's and mounts) -
mostly resulted in gradually corrupted and unrecoverable btrfs
partitions over time.

3 x raid 0+1 (btrfs raid 1 with 3 drives) - working well for about a month

~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!

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.

The comments on ceph only hold in my use case i.e., dont do it this way!
 After the experience and problems, I would still choose ceph for its
proper use case (its actually way cool!) - the ceph people do not
recommend btrfs for production use.

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.

BillK