[Cluster-devel] CMAN/DLM without SCTP

[David Teigland <teigland@redhat.com>]

On Tue, Feb 18, 2014 at 07:03:44PM +0530, Pratik Mehta wrote:
> Hi,
> I am trying to use a cluster with Pacemaker + CMAN on CentOS 6.4. The
> application that runs on the cluster includes a userspace SCTP stack.
> However CMAN loads dlm which loads the Linux kernel sctp module, which
> interferes with the userspace SCTP.
> 
> I do not have any GFS/locking requirements on this cluster. I use a 2 node
> cluster to failover a bunch of IP addresses.
> 
> I tried setting DLM_CONTROLD_OPTS="-r 0" and blacklisting sctp module.
> Didn't help since dlm depends on sctp and cman loads dlm.
> 
> In /etc/init.d/cman:
> errmsg=$( modprobe dlm 2>&1 ) || return 1
> errmsg=$( modprobe lock_dlm 2>&1 ) || true
> 
> As a hack: I modified the cman service to not load dlm and lock_dlm. The
> cluster seems working. However I do not know what additional functionality
> was broken when I disabled these. Though a hack: I am eager to know if
> someone sees an issue of running a production cluster with this.

That's a fine solution.  You might also be able to use
'service cman start quorum'.  The cman init script could probably
use some sysconfig option to either disable dlm/gfs2/etc or to
tell it to quit after the quorum step.

> Another options is to introduce a compile time flag in the DLM kernel
> module to not use SCTP.

Not long ago it was possible to avoid loading sctp, but people kept adding
sctp symbols and I didn't have to time to try to keep them out.  It would
be nice if that could be corrected again.

Dave