Exchange CCR cluster on VMware with iSCSI
A few weeks ago I got an assignment to review a colleague’s infrastructure design based on VMware.
The design was fine (because they used my design document as template :-) ) but one thing triggered me.
There was a special port group on one of the virtual switches names ‘MSCLUSTER’. No problem so far but I heard the client recently migrated to iSCSI storage.
The combination Microsoft Clustering Services (MSCS) combined with iSCSI triggered my alarm bells. As I recalled Microsoft Clustering on iSCSI is not a problem but Microsoft Clustering on VMware with iSCSI is not supported (by VMware).
So, I rejected the design based on this support issue.
This message was not well received, as it turned out they had just migrated their clustered Exchange servers and had been running this way for a while now. Proposing to the client to migrate again was no option. So they tried to question my findings. They had been running this setup without any problems and Exchange CCR clustering wasn’t real Microsoft Clustering because no disks were clustered, only the Exchange services.
A quick search told me that Exchange CCR clustering is based on Microsoft Cluster Service-Majority Node Set clusters, which do not require shared storage.
The last sentence, ‘which do not require shared storage‘, threw me off. Because I’m no Microsoft Clustering expert and certainly no Exchange guru I had to turn to my VMware resources.
My question was twofold.
One, Is Exchange 2007 CCR on VMware with iSCSI supported?
And two, If VMware doesn’t support this, is this going to change in the future?
So, is Exchange 2007 CCR on VMware with iSCSI supported? The VMware response is simple and straight forward.
– CCR is supported on iSCSI by Microsoft, but not by VMware.
– All clustered servers (including CCR/DAG) must use RDM disks, this is a VMware requirement, Microsoft doesn’t care.
– VMware only supports Fiber Channel for clustered servers even though CCR doesn’t use a shared disk model.
– For standalone servers (non-clustered), FC and iSCSI are supported by both VMware and Microsoft.
So VMware does not support Exchange CCR clustering on iSCSI but is this going to change in the future?
The response is promising. The Exchange team within VMware requested the vSphere product team to support iSCSI for CCR and DAG clusters. They also would like to remove the RDM requirement for CCR and DAG.
Response from the product team is that they are testing and will update the support stance in a future release.
Bottom line: Maybe in a future release VMware is probably going to support Exchange CCR and DAG clustering on VMware with iSCSI. At the moment it’s not clear in which future release this support will be added.
Personally I see very little advantages to use Exchange CCR over VMware HA or even FT for your Exchange servers.
OK, with Exchange CCR clustering you can back-up the offline node, no manual actions are needed for site recovery and data is available off-site.
This can all be achieved with alternate solutions like snapshotting, Site Recovery Manager and data replication.
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Hi Erik
I have done a very similar exercise… I looked at doing the same with Exchange 2007, then as soon as Exchange 2010 was release; which dropped CCR and replaced it with DAGs; move the design to EX2010. DAGs removes the need for MSClustering Services and uses replicated databases
Well, too bad that apparantly, VMware applies the same logic to DAG too:
http://communities.vmware.com/thread/265089
>As for shared storage; in a DAG environment you only assign the storage to a single VM, there is no shared storage so that should not be an issue there. However, per VMware support the data must reside on fibre channel attached storage, not VMFS or iSCSI.
This makes no sense to me.
Erik wrote : “OK, with Exchange CCR clustering you can back-up the offline node, no manual actions are needed for site recovery and data is available off-site.
This can all be achieved with alternate solutions like snapshotting, Site Recovery Manager and data replication.”
If you are using iSCSI storage like Dell EqualLogic you can protect your environment with snapshots and replicating it to another site fairly easy, but you could loose some data because you would need to take a snapshot every second to prevent data loss. Most companies 98% will not pay the price for 100% data protection and also this is not needed either. So yes you can protect your data with alternative like storage san sync or snapshotting but if you have to give a 100% guarantee on no data loss (will be very hard if the human factor is still in place ;-) ) you will have to use techniques that do log shipping or other methods to keep the data secure in two places. So I hope VMware starts supporting CCR clusters or DAG groups ( I would prefer the latter tho ).