[ClusterLabs] RHEL-6-7 - Is it possible to run the DLM without Kernel SCTP

[John Ruemker]

On 11/12/2015 04:39 AM, Stephen O'Kane wrote:
> Hi,
>
> My cluster setup uses GFS2 file systems, so I need DLM running.
> However I have an application that uses it's own SCTP for communication.
>
> This all worked fine until a recent upgrade to 6-7.
>
> It seems that in 6-6 the DLM was changed to use Kernel SCTP.
> The application I need will not run if Kernel SCTP is running.
>
> As far as I can tell it should be possible to switch the DLM back to
> using TCP, but I can't get it to work.
> The DLM now seems to have a hard-coded dependency on SCTP.
>
> The man page for dlm_controld states:
> "The  network protocol can be set to tcp, sctp or detect which selects
> tcp or sctp
> based on the corosync rrp_mode configuration (redundant ring
> protocol).  The rrp_mode none results in tcp. "
>
> In the output from corosync-objctl, the rrp_mode is none, so should it
> be running with TCP, not SCTP.?
>
> I also added <dlm protocol="tcp"/> to my cluster.conf, but DLM still loads SCTP.
> I also tried blacklisting the Kernel SCTP, but DLM will not start without it.
>
> I have searched the archives and some others have had the same, or
> similar issues, but they were able to avoid the problem by not
> starting DLM. With the GFS2 file system on my cluster I don't have
> that option.
>
> What config am I missing? Or is it no longer possible to run DLM over TCP?
>
> Thanks,
> TBSteve
>
>

I replied to your discussion in the Red Hat Customer Portal as well, but 
I'll repeat my reply here for anyone else that is interested.

The issue is not that DLM is still trying to use the sctp protocol even 
when you're explicitly setting protocol="tcp", but rather that the DLM 
module underwent a change in the RHEL 6 Update 6 kernel that caused it 
to now require loading of sctp no matter what configuration is in use. 
This is described further in the following knowledge solution:

cman is not starting after update to RHEL 6 Update 6 in a High 
Availability cluster with sctp blacklisted
https://access.redhat.com/solutions/1241283

As it mentions, Red Hat is considering changes to DLM that would remove 
the strict dependency on sctp unless it is specifically needed (that is, 
if its being used with RRP). If you would like to open a support case 
with us and reference that knowledge solution, we can link you to the 
bug report and keep you informed of progress as it moves forward.

Otherwise, I'm afraid if you absolutely cannot have sctp loaded, you'll 
have to revert to a RHEL 6 Update 5 or earlier kernel.


-- 
John Ruemker, RHCA
Principal Software Maintenance Engineer
Red Hat Global Support Services
Office: 919-754-4941