dan-572483 (4/10/2013)
What is the purpose of additional server nodes if you're not going to extend the SQL cluster there?
The whole idea of creating a multi node cluster is to make cluster administration easier. One 6 node cluster is easier to manage and uses less network name and IP resources than 3 x 2 node clusters.
Just because you have 6 nodes you do not necessarily want to extend your instance across all of the nodes, you'd generally leave at least one or as passive failover partners on hot standby for key instances.
dan-572483 (4/10/2013)
If the servers with SQL go down, you're down. (Unless the server is being used for other things, like a network fileshare.)
If i have 6 nodes with standard quorum setup of node majority with witness and 4 nodes fail then the cluster will be offline anyway. Whats the likelihood of 4 servers failing all at once, are they on a separate geographic site. you have to factor all this into your cluster design. Also, install 12 instances across 6 nodes and see how long the SP installer takes to run 😉
The SQL Server installation quotes the following
Installing a SQL Server 2008 R2 Failover Cluster
Then, you run Setup again for each node you want to add to the cluster.
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"Ya can't make an omelette without breaking just a few eggs" 😉