Need Help With 3 Node DAG Design (Full Version)

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worb68 -> Need Help With 3 Node DAG Design (4.Jun.2013 4:57:49 PM)

I need some help with my DAG and CAS Array design if possible to ensure optimum failover. I have the following:

3 Datacentres - 2 are production and one is DR
2 AD sites - the 2 production datacentres are in the first AD site and the second AD site is the DR site
F5 Load Balancer load balancing the connections to the CAS server's
Outlook 2007 Clients
All users on Exchange 2007 and will be migrated over

I'm planning a 3 Node DAG with a node in each data centre. Each node will be mixed role of HUB\CAS\MBX.

I want the DAG to replicate to all 3 sites so we can fail over mailbox access easy between each one if required. I also want client access for OWA and ActiveSync to be configured correctly on failover. The production CAS array will point to the production CAS servers and the DR CAS array will point to the DR CAS server.

Lets say the Production CAS is called PROD_CAS and has a load balanced IP of that points to DAG1 and DAG2 in the Production data centres. The DR CAS will just point to the CAS server in the DR site.

If we move all services to DR do I need to just change the IP for PROD_CAS to point in DNS to the DR CAS server?

Will the DAG replicate and work correctly for client access this way?

Have I missed anything? With a 3 node DAG if we loose 2 members then the DAG will be down. What is the easiest way to stop this from happening and to bring back up quickly?

Any help would be very much appreciated.

zbnet -> RE: Need Help With 3 Node DAG Design (5.Jun.2013 2:24:17 AM)

3-site DAGs aren't really very common at all. Most people consider 2-site DAGs to be complex enough; 3 sites makes things even more complicated.

When ever you stretch a DAG over multiple sites, it's usually best practice to have at least 2 copies of any given DB at each site, to prevent database reseeding over the inter-site links.

These are just a couple of thoughts, your design prompts perhaps more questions than an internet forum can do justice to.

worb68 -> RE: Need Help With 3 Node DAG Design (6.Jun.2013 3:05:40 AM)

Unfortunately I have 3 Datacentres and need a node in each one. There is no budget for extra servers and storage to be able to put 2 DAG nodes in the primary DC.

Any help anyone could provide would be very much appreciated.


zbnet -> RE: Need Help With 3 Node DAG Design (6.Jun.2013 3:37:48 AM)

Sometimes, when the requirement is so solid, and the factors totally immovable, then the task is impossible. If I say to you there are three people, and I want you to give an apple to each of them, but you only have 2 apples and you can't afford any more, then the task is impossible.

I want you to have a good, thorough read of this article and the two follow-on articles, especially part 3, and then see if you agree with me. And those only deal with the complexities of 2 sites, you've got three (although I agree not three user sites).

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