Cannot start DLM in TCP protocol

Latest response

I am running RHEL6-7 cluster and I cannot get the DLM to start without SCTP.

The man page for dlm_controld states:
"Kernel options
protocol
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.
Default: detect.

"

On the box the rrp mode is none, so it should result in tcp, but the dlm always loads the kernel sctp module.

"$> lsmod | grep sctp
sctp 267220 3 dlm
libcrc32c 1246 1 sctp
ipv6 335525 97 sctp"

I have also tried blacklisting the sctp module, and setting
in cluster.conf.

But no matter what I do I cannot get DLM to run without SCTP.

The reason is I have a 3rd party application that will not run if kernel SCTP running, so I need the DLM to run with TCP.
It all runs fine on RHEL6-4, but it won't run in 6-7.

Am I missing some config setting somewhere?

Responses

Hello,
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. Currently we are anticipating release of this modification in RHEL 6 Update 8, but that is tentative and subject to change.

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.

Let us know if you have any questions.

Regards,
John Ruemker, RHCA
Principal Software Maintenance Engineer
Red Hat Global Support Services

Thanks John.
Do you know if this fix will also be in RHEL7

We are pursuing the same changes in RHEL 7, so we're hopeful you should see those in a future release. However the newer implementation of the SCTP handling in DLM did not arrive in time to make RHEL 7 Update 2, so at the earliest it will be RHEL 7 Update 3.

I'll update the knowledge solution I linked to to also reference RHEL 7.

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