[dm-devel] RFC for multipath queue_if_no_path timeout.

[Benjamin Marzinski]

On Mon, Oct 21, 2013 at 09:17:31AM -0700, Frank Mayhar wrote:
> On Mon, 2013-10-21 at 11:05 -0500, Benjamin Marzinski wrote:
> > On Thu, Oct 17, 2013 at 12:03:10PM -0700, Frank Mayhar wrote:
> > > Dragging this back up into the light...
> > > 
> > > On Thu, 2013-09-26 at 19:49 -0400, Mike Snitzer wrote:
> > > > Frank, I had a look at your patch.  It leaves a lot to be desired, I was
> > > > starting to clean it up but ultimately found myself agreeing with
> > > > Alasdair's original point: that this policy should be implemented in the
> > > > userspace daemon.
> > > 
> > > I've found and fixed a couple of bugs but I would still like to know
> > > what issues you had with the patch.  As I said before, I would be more
> > > than happy to clean it up.
> > > 
> > > In the time since we had this discussion, by the way, we ran into a
> > > problem that a userspace daemon can't solve:  That of shutdown.  We ran
> > > into a number of failures in which systems were hung for hours.  It
> > > turned out that they were caused by a regular system shutdown.  Our
> > > backing store is network-based and networking was getting killed before
> > > applications (as is usually the case), leaving I/O outstanding on the
> > > device.  Since queue_if_no_path was set, the I/O wasn't dumped and our
> > > daemon was killed by shutdown very shortly thereafter so it couldn't
> > > recover (otherwise it would have cleaned things up).
> > > 
> > 
> > Was multipathd force killed? What was the default configuration
> > parameter "queue_without_daemon" set to?
> > 
> > If "queue_without_daemon" is set to "no", multipathd should disable
> > queueing when it is stopped. This was added specifically to avoid this
> > issue.
> 
> We don't run multipathd (we need our own daemon for various reasons) and
> we're also running an older kernel (based on 3.3), so we don't have
> "queue_without_daemon" yet.  (In fact, I don't see it on a cursory
> glance at dm-mpath.c; where is it implemented?)

It's implemented in multipathd, not the kernel, so won't be any help to
you then.

-Ben

> -- 
> Frank Mayhar
> 310-460-4042