Sometimes a two-node cluster configuration is not enough for your SQL Server, as you may want to create new SQL instances, which will reside in a different node than the existing SQL instances. So in this case you may want to add a 3rd or a 4th node to the SQL cluster.
Assuming you already have installed a SQL Server failover instance on two nodes and you now want to add a 3rd node, the steps to perform this procedure are as follows:
1. Setup Windows on the 3rd machine.
a. Patch Windows with the latest Service Pack.
b. Install the recommended hotfixes for a Windows cluster node (on all nodes).
e.g. Recommended hotfixes for Windows Server 2003 Service Pack 2-based server clusters
http://support.microsoft.com/kb/935640
2. Setup the public network of this new node properly, in the same subnet with the other two nodes.
e.g. if the two existing nodes have these IP addresses: 192.168.2.101 & 192.168.2.102, then give an IP address in this range: from 192.168.2.1 to 192.168.2.255
Also setup the private network properly, to match the subnet and IP mask of the other two nodes’ private network.
Note: Setting up the networks of a cluster node are documented in pages 6-12 & 30-32 of this whitepaper: http://www.microsoft.com/downloads/details.aspx?familyid=96F76ED7-9634-4300-9159-89638F4B4EF7&displaylang=en
3. Join the new node in the same domain with the other two nodes.
4. Document what shared disks the other two nodes can see. The new node need to have access to these shared disks too.
5. Logon in one of the other two nodes and open the cluster administrator console. Perform these steps:
a. Click File, click New, and then click Node.
b. The Add Cluster Computers Wizard will start. Click Next.
c. If you are not logged on with appropriate credentials, you will be asked to specify a domain account that has administrative rights over all nodes in the cluster.
d. Enter the machine name for the node you want to add to the cluster. Click Add and then click Next.
e. The Setup wizard will perform an analysis of all the nodes to verify that they are configured properly.
f. Type the password for the account used to start the cluster service.
g. Review the summary information that is displayed for accuracy. The summary information will be used to configure the other nodes when they join the cluster.
h. Review any warnings or errors encountered during cluster creation, and then click Next.
i. Click Finish to complete the installation.
Note: These steps are documented in page 29 of this whitepaper: http://www.microsoft.com/downloads/details.aspx?familyid=96F76ED7-9634-4300-9159-89638F4B4EF7&displaylang=en
Now the third node has been added to the cluster. So now the cluster group should be able to failover properly to the third node as well.
6. However we still need to configure the SQL Server instances so that they are able to failover to the third node as well. The process for adding or removing a node is similar to setting up a new clustered instance of SQL Server:
a. Logon to one of the old nodes where SQL server is already installed.
b. Go to Control Panel and open Add or Remove Programs.
c. Select Microsoft SQL Server 2005. Choose which SQL instance you will configure. Then click Change.
d. Setup launches.
e. At the Change or Remove Instance page, select Maintain the Virtual Server.
f. Go through the menu pages and in the Cluster Node Configuration page add the third node, e.g. like seen in this screenshot:
g. All nodes except the node from which you are installing, should be displayed in the Selected nodes list.
You need to perform these steps one time for each instance you have (so in your case this means that you have to add the third node three times, one for each instance).
Note: These steps are documented in page 25 of this whitepaper: http://www.microsoft.com/downloads/details.aspx?FamilyID=818234dc-a17b-4f09-b282-c6830fead499&displaylang=en
So although this is a delicate procedure, it is not very complex and if you perform this during a scheduled downtime you should not face any strange issues.
Disclaimer
This is a personal weblog. The opinions expressed here represent my own and not those of my employer. The steps are provided “as is” without a warranty of any kind.