[Linux-cluster] Can same cluster name in same subnet?

Chrissie Caulfield ccaulfie at redhat.com
Tue Mar 31 07:29:45 UTC 2009

Vu Pham wrote:
> Chen Ming wrote:
>> Hi,
>> I setup two cluster in same subnet, using the same name, it seems the
>> later cluster can not startup. I try to start cman but failed. My
>> environment is RHEL 5.3.
>> My question: Is it possible to use the same cluster name in same subnet?
> From the man page of cman
> -----------------
> Cluster ID
>        The  cluster  ID number is used to isolate clusters in the same
> subnet.
>        Usually it is generated from a hash of the cluster name, but it
> can  be
>        overridden  here if you feel the need. Sometimes cluster names
> can hash
>        to the same ID.
>          <cman cluster_id="669">
>          </cman>
> -----------------
> So I think you either have to use different names or to explicitly
> specify different cluster_id.
> But why do you have to have the same cluster name in the first place ?

Bear in mind that using the same cluster name is highly dangerous if you
are using GFS with storage that is shared between the clusters.

GFS checks the cluster name before mounting and if it matches the
current cluster assumes it's OK to carry on. If two clusters have the
same name then that means two independent clusters could mount the same
GFS volume. The result of that would be a totally corrupted filesystem.


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