[Pacemaker] CMAN integration questions

Vladislav Bogdanov bubble at hoster-ok.com
Thu Dec 23 04:41:36 EST 2010

Hi Andrew,

It was a big surprise for me to see all pacemaker-specific bits removed
from dlm and gfs2 in cluster-3.1.0, so there is currently no way to use
pacemaker on f13 with dlm/gfs2/clvm but without cman.

So, would you please bring some light on details of integration with cman?

Especially I need to understand how pacemaker integrates with cman's
fencing/dlm subsystem:
*) Do I need to configure fencing in both cman and pacemaker? Or
pacemaker should be (is) able to fence nodes via cman's fenced interface?
*) Is there a way to postpone any (monitor too) operations on specific
resources until fencing domain stabilizes? Otherwise I probably need to
configure huge timeouts for operations and then cluster becomes not
smart. Under 'specific resources' I mean LVM VGs and LVs together with
gfs2 filesystems. I currently have problems with fence domain stability
(https://bugzilla.redhat.com/show_bug.cgi?id=664958) that's why I
noticed that LVM and Filesystem RAs go mad while DLM is being frozen.

>From what I see, relying on cman's quorum is not sufficient when DLM
comes to play, pacemaker needs to know the state of fencing system as
well. I started to think about monitoring of that subsystem from within
RA which then sets some cluster/node attributes, but realized that this
won't help - more tight integration is needed.

And one more question/proposal about CMAN/DLM/GFS2:
now it is possible to use DLM/GFS2 on nodes without pacemaker installed.
I mean, if I configure additional node in cman but have no pacemaker
started on that node, then I'm still able to mount GFS2 on that node.
One minor problem is that rest of pacemaker cluster waits for that node
to start pacemaker too. So all clone resources are extended with one
more instance which "will never be started". On the other hand I see in
pacemaker sources, that there are two types of nodes: member and ping,
and all resource processing is done only for nodes which are members.
Would it be too hard to add one more node type, f.e. "arbiter" (it
participates in cman cluster so it influences quorum/fencing), which is
only valid for CMAN clusters and is not supposed to run any resources?
Then clones will not try to extend on that arbiter nodes, fewer
resources, less computations, cleaner 'crm status' output.

Could you please comment on this?


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