[Linux-cluster] Quorum disks and two-node clusters

[Lon Hohberger]

On Tue, 2006-10-10 at 10:21 +0200, Pena, Francisco Javier wrote:
> [...]
> 
> > When the score drops below 1/2, qdiskd advertises to CMAN 
> > that the "quorum device" is gone.  CMAN loses local votes and 
> > the node becomes inquorate.  There's a bug in qdisk that 
> > prevents qdisk from rebooting the node the way it is 
> > documented to upon this loss of score.  (This is already 
> > fixed in CVS.)
> > 
> > -- Lon
> > 
> 
> Lon, 
> 
> Do you know if there are any plans to release an updated cman package, including this bugfix, before U5? My company is planning to start implementing GFS, and this would definitely be required for us.
> 
> Regards,
> 
> Javier Peña

Hi Javier,

I do not think there is a plan to release the fix early, but that could
change at any time.  Note that because the changes were very simple, you
can use the checked-out version from CVS and it will work on U4+errata
as a drop-in replacement.

I am interested to know how you are going to use qdiskd such that this
is a show-stopper for your organization.

The only case where the lack of rebooting becomes problematic is if you
have heuristics which are not concerned with network connectivity (note:
this is a perfectly valid case, of course).

That is, if two nodes see each other, but one thinks it is inquorate,
the quorate node will *not* fence the inquorate node, and... well,
things will not work very smoothly (this is the case where a reboot is
needed).

In network outages (one of the things qdiskd was designed to help with),
the nodes will not see each other, so the node which still thinks it is
quorate will fence the inquorate node, and the cluster will cleanly
continue.

-- Lon