CAS Array - DR Site

Hi Experts,

I have 8 Exchange servers in total.

4 in Site A
4 in Site B

Each site consists of:

2 Mailbox servers in a DAG

I have a CAS Array for the live site.

Cas name:

Site: London
FQDN: mail.domain.local
Members: EXCH01, EXCH02


I will be looking to fail this site over, changing DNS records to point what I need to the servers in Site B.

My question is:

Do I simply need to add the 2 servers in Site B, into the same CAS array and edit the Site location of the Client Access Array when I swap over?
The DAG is stretched between the 2 sites, so only 1 site will be operable at one time. (which is fine).

Out of curiosity too, is there a way of creating an Active/Active site going forward, so we can utilize the servers better?

I'm thinking: I would need to create additional databases and split up the mailboxes into different databases and split these across Mailbox Servers. Assign the mailbox servers to a specific CAS array and set up autodiscover on these servers to point to the CAS NLB in Site B?

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Madan SharmaConnect With a Mentor ConsultantCommented:
Here are the answers straight to your questions:-

1. You can configure your Site B with same name spaces without have any issue and in case of site A fail-over you have to change your DNS entries to SiteB. It will word as active/passive site resiliency solution with same name specs and certificate .
Note:- if you are going to use this you must have a low TTL value for your DNS. So that it can take place soon in case of failure

2. Yes you can deploy Active/Active Site resiliency model with exchange 2010

3. if you are going to deploy active/active model then you need to create Second DAG and split up the mailbox between them

check this 3 part  fantastic blog from Henrik Walter wit all the details:-
Neil RussellTechnical Development LeadCommented:
Exchange 2010 has a whole new aproach to DR compared to previous versions. I would suguest you start by FULLY reading and understanding the following.
MarkMichaelAuthor Commented:
Sorry, but I don't post here to be pointed to articles. :)

I have set up the rest of the DAG for site resilience. I'm simply looking for help with the CAS array and answers to my questions above.

What do you use to create the CAS Array? A hardware loadbalancer? Windows NLB (Network Load balancing)? DNS Round Robin?
The way you are "clustering" the CAS-servers in one location now will have impact on how you can move the client access to the other location...
MarkMichaelAuthor Commented:
I have
2 CAS servers in SiteA
They are using mail.domain.local as their ClientAccessArray

I assume I will add the 2 CAS servers in SiteB into membership of the mail.domain.local ClientAccessArray and set the Site name to SiteB.
Possibly removing the SiteA members from the CAS Array once we have failed over?
Am I able to edit the current config of the cas array, or will i need to delete and re-create it?

I am using a Windows NLB on the CAS servers.
I have TMG for Reverse proxying Servers from the Internet. The A record for these will be changed on public DNS servers which we host for our site. TTL is set to 20 seconds too.

Thanks for the help!
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