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I currently have a single default instance of SQL2017 Standard on a 2-node cluster. Against my preference, I need to setup a second instance on the cluster (the new database requires some users to have sysadmin so they can't be hosted alongside other databases on the existing instance :-( )

On the existing cluster, only the Active node is licenced.

When I install a second instance, do I HAVE to use a separate set of disks, or can it be installed on the same disks as the default instance? (I'm not even sure if it is possible, let alone whether it is preferable) Am planning to host BOTH instances on a single node - resource requirements are not high, so can be managed.

My concern is that one of the instances 'could' fail over to the second node. But the second node is not licenced, so am not allowed to run an instance on each node (though I believe I do have a short period to fail it back).

Presumably I need to implement some monitoring to alert me if EITHER instance fails over, and get it failed back ASAP.

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When I install a second instance, do I HAVE to use a separate set of disks, or can it be installed on the same disks as the default instance?

Yes you need to have a separate set of disks for the new instance.

I'm not even sure if it is possible, let alone whether it is preferable) Am planning to host BOTH instances on a single node

That is not a bad idea, lot of people do and we call it as multi-instance cluster. Both the instances would be on same node in your case. They can also be on different nodes but you need to look at licensing part then.

My concern is that one of the instances 'could' fail over to the second node. But the second node is not licenced, so am not allowed to run an instance on each node

In your scenario you have 2 instances on same node, this is fine since 2nd node is purely passive. BUT if a failover happens for "an" instance on 2nd node which is not licensed then you would have an instance running both on 2nd node and 1st node, this is a license violation if you run this scenario for long time, unless you immediately move it back such that both instances are on same node. The term "immediately" here means as soon as possible, MS is not going to charge you if let us say for hour you run 2 different instances on 2 different nodes.

PS: I am not a licensing expert but you should get this verified from local licensing expert of your region.

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Thanks for the reply. The obvious solution is to install the second instance on separate disks. But this DOES cause a licensing issue :-( I've just checked:

  • In the event that a passive instance of SQL Server becomes active for any reason, the primary SQL Server 2017 license is dynamically reassigned to the newly active server via the License Mobility within Server Farms SA Benefit, and now assumes all active workloads.

  • In the case where individual SQL Server instances are failing over independently from each other, each SQL Server OSE running an active SQL Server instance requires separate licenses.

So.....if ONE instance fails over, then since we are running BOTH nodes, they BOTH need to be licenced. I can't find any reference to any 'time-period' during which I can fail-back without penalty.

If BOTH instances failover, then we are ok, since the licence switches to the second node.

But.....how do I ensure that BOTH instances failover, and not just one of them?

Hence, my question about whether both instances could be put on the same set of diks?

OR.....is there some configuration available in Windows Clustering to ensure that BOTH SQL Server services failover together???

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