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Service guard

Occasional Advisor

Service guard

Can we use SAN disk for Cluster lock in the Extended Distance cluster service guard  SGE RAC Cluster in HP ux 11:31

Patrick Wallek
Honored Contributor

Re: Service guard

Here is what the best info I can find regarding cluster lock disks.


Understanding and Designing Serviceguard
Disaster Tolerant Architectures Sixth Edition


Configurations with two data centers have the following additional requirements:
• In orderto maintain cluster quorum afterthe loss of an entire data center, you must configure
dual cluster lock disks (one in each data center). Since cluster lock disks are only supported
for up to four nodes, the cluster can contain only two or four nodes. Serviceguard does not
support dual lock LUNs, so lock LUNs cannot be used in this configuration. When using
dual cluster lock disks, there exists a chance of Split Brain Syndrome (where the nodes in
each data center form two separate clusters, each with exactly one half of the cluster nodes)
if all communication between the two data centers is lost and all nodes remain running. The
Serviceguard Quorum Server prevents the possibility of split brain; however the Quorum
Server mustreside in a third site. Therefore a three data center clusteris a preferable solution,
to prevent split brain, and the only solution if dual cluster lock disks cannot be used, or if
the cluster must have more than four nodes.


It would probably be best to use a quorum server, but that requires a server in a 3rd location.

Patrick Wallek
Honored Contributor

Re: Service guard

And here's a good link for the difference between a lock LUN and a lock DISK.  Duncan Edmonstone's response is the most correct one.  Kindly ignore my response in that thread.