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In a two-node Windows Server 2008 failover cluster, is it required that the machines be identical? We're looking to utilize existing hardware to reduce downtime using one very fast server and one only moderately fast server, both Dell PowerEdges but of different generations.

I've found the following suggestions that you should use matching hardware, but will we be able to achieve our goals of increased availability using different servers? And if so, what types of issues should we look out for with this type of configuration?

From MS TechNet: Appendix A: Failover Cluster Requirements

We recommend that you use a set of matching computers that contain the same or similar components.

From Windows Server 2008: Inside Out

You should use identical hardware in all clustered servers. Using identical hardware components makes the configuration easier to manage and can eliminate potential compatibility issues.

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3 Answers 3

up vote 2 down vote accepted

They are not required, but as you have quoted, they are recommended.

I have seen clusters where one half is a physical machine and the other is a VM.

edit

For support reasons in most cases you should not, but during a failover, as long as both sides of the cluster are able to handle the resource shift, you should be fine.

If all sides of the cluster have the necessary hardware, and resources, to handle a failover, it would be perfectly acceptable.

You can also run cluster validation to ensure everything will be fine.

You might want to make sure that the configuration you are running is supported though, since your server vendor and/or Microsoft might refuse support if it is not.

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Thanks for the note. I've expanded the question a bit since I'm pretty much answering the question with my cites. –  boflynn May 14 '09 at 16:54
    
nice. i'd be interested in any discussion on the trade offs of physical vs VM. –  chickeninabiscuit May 14 '09 at 16:58

Yes, you can achieve your goal of HA with the provisos you've already specified about support. Potential issues that I've seen personally:

  • Different hardware leading to different drivers causing an application conflict, memory leak, etc. on one side and not the other.
  • Different performance characteristics, the slower one which may be considered unacceptable.
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It will be possible to create the cluster, however the Cluster Validation wizard will show warnings. With-out a 'green' cluster validation Microsoft will not support the cluster, and some other Cluster serverices (SQL 2008 comes to mind), will not even install on top of the cluster without first passing the validation.

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