[Linux-cluster] cman bad generation number

Patrick Caulfield pcaulfie at redhat.com
Thu Jan 6 08:47:19 UTC 2005

On Wed, Jan 05, 2005 at 02:19:01PM -0800, Daniel McNeil wrote:
> Do DLM and CMAN use a common communication layer?

No. They should, but the communications in CMAN is primitive and not up
to supporting the high levels of traffic that the DLM can generate. CMAN uses
its own "reliable multicast" system whereas the DLM uses TCP. The disparity is
really only because CMAN needs to do cluster-wide broadcasts but the DLM only
ever needs to talk to single nodes at a time (per message).
> I was expecting that they would since having multiple
> interfaces for redundancy would be something they
> would both want.  DLM should just want to be able
> to send messages to other nodes and shouldn't care
> how it gets there.  I was expecting this to be
> part of CMAN since it should know which interfaces are
> connected to which nodes and their state.  It could
> also load balance on multiple networks.  Is there a
> description of how multiple interfaces are handle today?

The short answer is "rather badly". CMAN handles dual interfaces by a simple
failover if messages go missing. DLM gets the interface information from CMAN
but because of the nature of TCP the failover isn't nearly as clean



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