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Re: [Linux-cluster] CMAN/DLM without SCTP



On 18/02/14 13:33, 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.

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

Is there any other way?


You should be fine like that. The things that use the DLM are GFS and clvmd so if you don't use either of those then not having the DLM running won't have any effect. You'd soon see error messages if anything you were running depended on it .. I hope!

I suppose we didn't really envisage alternative SCTP stacks when the DLM was written and it's never come up as a problem before.

Chrissie


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