May 7, 2008 at 7:06 am
I have a need to add a second Sql instance to an existing cluster. However I read in this article http://www.sql-server-performance.com/articles/clustering/clustering_best_practices_p1.aspx
that this is not recommended. Does anyone know why this is or what problems I may encounter?
Its is running Sql 2005 on a 64 bit windows Server 2003.
May 7, 2008 at 8:37 am
So I take it you have a two node active/passive setup, having one instance installed on a two node cluster?
May 7, 2008 at 10:06 am
yes thats correct, one active one passive for the default instance
May 7, 2008 at 10:46 am
OK, so you have a couple of options here. If you think one node can handle both intsances, there should not be a prolem. you would end up with an active/active cluster with one instance running on each node. then if you have a failure, both instances would be running on one node. This is why you need to ensure one node can handle tthe load of both instances.
With enterprise edition, you have an additional option of setting up an N+1 cluster, meaning you would have 2 active nodes and 1 passive node. This is the safest way to handle this because you always have a passive node ready to jump in for an active node. Use this option if you don't think 1 node can handle both instances.
In short, you just need to plan for capacity for each node as you would with a standalone server with multiple instances and make sure if you loose a node, that the nodes left in the cluster can handle the load.
May 8, 2008 at 2:37 am
Thanks for the response. Our cluster setup is that we have one physical server for the active node and one virtual server for the passive node.
Ideally I would like to make the second instance, active on the physical server. I think the physical server can easily handle the load of two instances. Is this configuration possible?
May 8, 2008 at 10:53 am
Why not add a second virtual machine to the cluster, run an instance of SQL on each, and have the virtual machines normally on opposite nodes. This way both physical servers are kept busy.
That's what we do at my site.
You would need to ensure that you set up SQL Server memory to be limited so that if one physical box does fail and both instances are then running on the standby node that there is enough RAM for both (in other words make sure one of them doesn't hog all the RAM if it is first to start up).
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May 8, 2008 at 12:04 pm
you could certainly have both instances running on the physical box if it can handle both, but the previous suggestion isn't bad either.
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