Re: Is stability a joke?

[Lionel Bouton <lionel-subscription@bouton.name>]

Hi,

On 12/09/2016 14:59, Michel Bouissou wrote:
>  [...]
> I never had problems with lzo compression, although I suspect that it (in 
> conjuction with snapshots) adds much fragmentation that may relate to the 
> extremely bad performance I get over time with mechanical HDs.

I had about 30 btrfs filesystems on 2TB drives for a Ceph cluster with
compress=lzo and a background process which detected files recently
written to and defragmented/recompressed them using zlib when they
reached an arbitrary fragmentation level (so the fs was a mix of lzo,
zlib and "normal" extents).

With our usage pattern, our Ceph cluster is faster with compress=zlib
instead of the lzo then zlib mechanism (which tried to make writes
faster but was in fact counterproductive) so we made the switch to
compress=zlib this winter.

On these compress=lzo filesystems, at least 12 where often (up to
several times a week) corrupted by defective hardware controllers. I
never had any crash related to BTRFS under these conditions (at the time
with late 3.19 and 4.1.5 + Gentoo patches kernels). Is there a bug
somewhere open with kernel version affected and the kind of usage that
could reproduce any lzo specific problem (or any problem made worse by
lzo) ?

Lionel