Quorum server in RAC

[ASME]

Hello there,

I am wondering is quorum server is required in Oracle RAC setup?

as in RAC instances will be running on all the nodes and there is no failover of the service groups.

Reg,
Asme

[Duncan Edmonstone]

Asme,

Are you talking about a RAC database on Oracle Clusterware, or RAC on Serviceguard Extension for SAP?

For clustewrae, Oracle uses cluster interconnect for heatbeat and the OCR and voting disks for quorum resolution.

For serviceguard, you still need some form of quorum, be it a cluster lock disk, a cluster lock lun, or a quorum server, as you still may need to arbitrate when a cluster reforms if it is unable to achive the usual quorum of >50% of cluster members.

HTH

Duncan

[Duncan Edmonstone · Accepted solution]

bah I meant Serviceguard Extension for RAC, and nor for SAP!


HTH

Duncan

[ASME]

thanks Duncan,

I am talking abt the Mcsg RAc ext for oracle.

If the oracle cluster membership is managed by the oracle and the all the nodes are conencted to a s/w then why we need a arbitrator ?

if the nods are connected in linear fashio then it could be the issue but if there is s/w then why we need the quorum ?

Reg,
Asme

[Duncan Edmonstone]

Clusterware membership might be managed by Oracle, but in a Serviceguard Extension for RAC (SGeRAC) cluster, Oracle clusterware is effectively "subservient" to Serviceguard - it's Serviceguard that will decide who is in and who isnb't in the cluster.

So the normal rules of serviceguard clustrers apply - at the point at which a cluster reformation event occurs:

-any node or group of nodes who can still "see" more than 50% of the cluster nodes will continue working

-any node or group of nodes who see less than 50% of the cluster nodes will be forcibly ejected from the cluster by a TOC (reboot).

-if any node or group of nodes can only see exactly 50% of the nodes in the cluster then arbitration needs to happen - to do therwise would be to risk data integrity as you can't know what the other nodes ar doing. Standard methods of arbitration are cluster lock disk, cluster lock LUN, or quorum server. Each have various constraints but you must use one...

See the manual here for more details:

http://docs.hp.com/en/B3936-90122/ch03s02.html#babggaac

HTH

Duncan

[Emil Velez]

Oracle RAC running with ServiceGuard only requires a quorum server or lock disk if the cluster requires a lock disk. IN otherwords if it is a 2 node cluster

[Duncan Edmonstone]

Emil,

Strictly speaking you are correct - only 2-node clusters _require_ a cluster lock, but we do _recommend_ a cluster lock for larger clusters as well. I'd certainly never build a cluster without one. Here's the relevant text from the manual:
----------------
A one-node cluster does not require a lock. Two-node clusters require the use of a cluster lock, and a lock is recommended for larger clusters as well. Clusters larger than four nodes can use only a quorum server as the cluster lock. In selecting a cluster lock configuration, be careful to anticipate any potential need for additional cluster nodes.
----------------

This is from the manual here:

http://docs.hp.com/en/B3936-90122/ch04s04.html

HTH

Duncan

[Thomas J. Harrold]

We have configured a linux quorum server in our SGeRAC environment, and it has performed well for nearly 1.5 years. I recommend a script that will run a cmviewcl and monitor for the status of the quorum service - as an added check in case your quorum service goes down.

We didn't use a SG cluster to run our quorum service, but are rethinking that after someone kicked out a power cable.

-tjh

[Emil Velez]

Remember that the quorum server can be a source of failure but is only used during a cluster reformation when a node is lost or cannot communicate.

If the qs fails fix it. If the qs fails and a node fails thats 2 failures and HA is mostly about single points of failure.