CCR/SCR design query


I had a theortical query on CCR/SCR in Exchange 2007 that I was hoping someone could help me with.

Let's say I have a Main Office site in London, UK. The DR site is in Swindon, UK. There is a good WAN link between the two sites.

From what I understand, a good DR strategy for Exchange 2007 would be:

- Have a CCR/SCC cluster located in London with Hub Transport and CAS servers.
- Have an SCR target located in Swindon, also with Hub Transport and CAS servers.

However, how about this idea:

Have just one CCR cluster, but with one node in London and one node in Swindon (with HT/CAS in both locations).

Would this work? I can't see any reason why not and it would actually cut down on hardware expenditure? The amount of data replicated is still the same isn't it?

Secondly, is there actually any need to have a CAS server in the DR site?

Thirdly, wouldn't the CCR only method work better considering we'd need to upgrade to 2010 at some point, and 2010 does not support SCR/SCC?
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Glen KnightCommented:
Ok what you really need is an SCR (Standby Continuous Replication) cluster.
This is designed for DR.  Have a read of:

what ever you do now will not he replicated for Exchange 2010 as we now have the Database Availability Group (DAG) I have written an article on it here:

and since there is no in-place upgrade to Exchange 2010 you would need to build a new cluster and migrate to it.

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Jamie McKillopIT ManagerCommented:

You can setup your CCR cluster so that one node 1 is in one site and node 2 is in another site but there are some pitfalls. You would need to have both sites in a single AD site. You would need/want a CAS server in each site for DR. The reason you would want a CCR node at each site is in case one whole site goes down. It does you no good to have the mailbox server up but no CAS server available. You would also need a Hub transport server in each site for the same reason.

Here is a good explanation of some of the problems you would encounter with a multi-site design -


You're correct. Exchange 2010 doesn't support CCR/SCR, which were complicated to say the least. 2010 simplifies the database model greatly into the Database Availability Group/Mailbox Copy structure, as demazter already indicated.

There are a number of considerations you need to take into account with cross-site CCR. There are placement issues for the File Share Witness (if you only have two nodes and an FSW and your FSW site burns down, the backup site won't have quorum so the cluster will not start automatically). Similarly, you won't get true "failover" (within a matter of minutes) because the DNS change for the cluster must be replicated. You must also extend the Active Directory site to the backup data centre, since CCR nodes cannot be deployed across AD sites.

That said, what you MIGHT want to consider is a mix of CCR and SCR, or simply opting for Exchange 2010 DAG. You can deploy a mix of CCR and SCR, with intra-site CCR backed up by SCR to another site for off-site backup purposes.

Note also that SCR requires manual admin intervention to fail it over, whereas CCR provides typical clustering capabilities with automated failover in the event of an outage.

I would seriously suggest you consider Exchange 2010 DAG. The deployment model has been vastly improved. You can also save on licensing and hardware by deploying roles other than the Mailbox role on the DAG Mailbox Server (you are restricted to only the Mailbox role on a CCR/SCR host).

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