[Linux-cluster] RHEL6 HA addon

Digimer linux at alteeve.com
Thu Feb 24 16:24:30 UTC 2011

On 02/24/2011 10:44 AM, Richard Allen wrote:
> Hi all
> I notice in the Release Notes for RHEL6 that many changes have been made
> to the Cluster Suite (HA Addon) but I am unable to find any mention of
> how the new suite does heartbeat.
> In previous versions the Cluster could only do heartbeats (node
> intercommunication) on one network link and for redundancy the only
> option was to use bonded network devices.
> There was a way to add a second heartbeat using altnode directives in
> the XML config file but that always felt a bit hackish and was only
> limited to only one altnode, giving two heartbeat paths.
> So I would like to ask how RHEL6 does this.  If I have nodes with 4 10Gb
> NIC's, one connected to an admin network, another to a Database network
> and one to the Application network and the last one connected directly
> to the other node with a crossover cable, can the cluster now use all
> possible paths to communicate to the other nodes or will one of those
> paths become a single point of failure in the cluster?
> I'm used to using Clusters like HP's ServiceGuard where I can easily
> define which links to use as heartbeat.  It can even use a serial
> connection (in a two node cluster) as a additional heartbeat and I have
> always felt this is quite a big limitation in Red Hat's cluster suite up
> to RHEL6 atleast.
> Thanks in advance
> Richard.

Hi Richard,

  Can I assume that you are talking about High Availability in general,
as opposed to Heartbeat specifically? If not, the rest won't be too

  As you know, the 'altnode' parameter is how you assign a second link.
This is still the case (as is bonding to get more links, but that
requires common subnets which you don't have).

  Corosync is used as the cluster communication layer (as opposed to
openais from RHEL 5.x). It supports one or two interfaces for "totem"
communication. If the main fails, the second link will be used
automatically. However, when the main is restored, totem must be
manually moved back to the original link.

  So in short; as it was in 5, so it is in 6. That said, the 'altname'
is perfectly valid way of removing that SPF. :)

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