MS SQL cluster - How many Instances? And what entails?

We have a recently installed MS SQL 2012 cluster.
- How many more instances can be added to it?
- Does each instance requires a separate SQL license?
- How many separate SAN drives will we need for each instance? Currently we have: 1. database 2. log 3. TempDB 4. Backup. Perhaps Backup drive can remain same, but what about TempDB drive? It seems, minimum two new SAN disks be needed?


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Scott PletcherSenior DBACommented:
It depends on the licensing model.

If you have Enterprise Core licenses, you can add as many instances as you want.

It depends on the drive speed.  You do not have to isolate tempdb to separate luns (really, you don't), if you're other drives are fast enough so that their IOPS can handle the total load.

For recoverability, you'll want the log and data files for the same db on different (physical) drives/raid sets if at all possible.  You can put the backup files with the log files if you really need to.

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AkulshAuthor Commented:

Thanks for replying.
Since it is a SQL cluster which requires enterprise license, we are of course using it.

So we can add 3 more instances easily. Is there any Microsoft link that affirms this? Thanks.

Scott PletcherSenior DBACommented:
Here's some official MS text on this:
With the SQL Server 2014 Enterprise Edition, when you have licensed all physical cores on the server, you can run an unlimited number of instances of the software in a number of OSEs (physical and/or virtual) equal to the number of core licenses assigned to the server. For example, a two-processor server with two cores per processor—fully licensed with eight core licenses (assuming a core factor of 2 in the SQL Server Core Factor Table)—could run SQL Server software in up to eight virtual machines, regardless of the number of virtual cores allocated to each virtual machine.

With the addition of Software Assurance (Software Assurance) coverage for all Enterprise Edition core licenses (when the server is fully licensed), your use rights are expanded, allowing you to run any number of instances of the software in any number of OSEs (physical or virtual). This enables you to deploy an unlimited number of virtual machines to handle dynamic workloads and fully utilize hardware computing capacity. Note: This benefit ends when Software Assurance coverage expires.
AkulshAuthor Commented:
I presume it also applies to SQL 2012 enterprise. Thanks.

Scott PletcherSenior DBACommented:
I believe it does.  To 2012, but not before that.
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