People,
Date: Mon, 21 Mar 2016 15:02:02 -0600
From: Chris Murphy <lists@xxxxxxxxxxxxxxxxx>
To: phil@xxxxxxxxxxxxx, Community support for Fedora users
<users@xxxxxxxxxxxxxxxxxxxxxxx>
Subject: Re: Discourse - DeviceMapper causing corruption?
Message-ID:
<CAJCQCtSCPQRQsecq0+dzEKdNjEDfBzaDavOOV_e_ARL6LjgkDg@xxxxxxxxxxxxxx>
Content-Type: text/plain; charset=UTF-8
On Mon, Mar 21, 2016 at 1:03 PM, Philip Rhoades <phil@xxxxxxxxxxxxx>
wrote:
People,
I had a couple of issues to sort out with installing the Docker
Discourse
app and while that was being done people made these comments:
"Devicemapper is non starter, fails spectacularly under load and
causes
corruption. We block setup if we detect devicemapper. You need aufs or
another better supported docker filesystem."
- which was not true - it did install without resorting to aufs.
also:
"Redhat team get very upset when we mention that it just does not work
for
us, but release after release they say there are no bugs left, and
each time
we keep seeing Discourse users complain about corruption due to device
mapper."
Any comments?
On the one hand, I'd say, talk is cheap, show me the bug.
On the other hand, having blown up thinly provisioned pools quite a
few times early on, I basically couldn't handle how non-deterministic
the blow ups were, and how difficult the LVM and devicemapper tools
are to understand the state of the pool, and fix it. So I gave up and
went down the Btrfs path just because I understand it better, and
there are only so many rabbit holes one has time and interest to go
down.
For a good bug report you either need a way to debug it, i.e. you need
familiarity with that thing you are debugging. Or you need a concise
set of reproduce steps (and a list of versions) so someone else, like
a dev or more experienced user, can reproduce that environment and
steps and debug it. Without one of those two things at least, I think
it's unreasonable to say "hi this is busted" and then just walk away.
aufs is just not workable in my opinion because it's not in the
mainline kernel. So any sense of portability can't be that important
if you're going to depend on aufs. There are plenty of bugs to go
around at this point, between overlay(fs), btrfs, and devicemapper
although I think by now most of the devicemapper stuff is probably the
more stable of the three (?) just a guess really. I had 500+ container
states as Btrfs subvolumes and never ran into a Btrfs related problem
though. What are the CoreOS folks using? Overlay or dm?
I had another response on the Discourse forum:
"It's probably this bug, devicemapper seems to be unable to free deleted
files until you delete the container:
https://github.com/docker/docker/issues/188672
Which is catastrophic for any long-lived server that uses temporary
files in any capacity at all."
Does that also make sense to more clued-up tech people than me?
Regards,
Phil.
--
Philip Rhoades
PO Box 896
Cowra NSW 2794
Australia
E-mail: phil@xxxxxxxxxxxxx
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