Exchange 2010 DR solution

I am little puzzled about creating an Exchange 2010 DR environment in case if production site goes down.

Here is setup we have:

2 Active Directory sites in 2 states connected with 50MB pipe
All servers including Exchange is in SiteB
All users are in SiteA

We have 2 Exchange Server 2010 in a DAG, 1 CAS and 1 HUB.  Users connect to CAS using server name and all is well so far.

Now management want to have a DR solution

I am thinking to have one Exchange server with Mailbox/CAS and HUB and part of the DAG in SIteA. in case if we need to fail over, how would i redirect users to new CAS? is this the best solution? Please let me know your opinion!
Thanks
stratomanAsked:
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Adam BrownSr Solutions ArchitectCommented:
In order to redirect users to the new CAS, you would do 1 of two things:
1. Utilize a Hardware Load Balancer - This would allow both CAS servers to handle client access, and if one fails the other takes over. This, of course, requires both servers to be in the same AD site. If you have a second AD site, you have to use the next option.
2. When a failure happens, reconfigure the DNS records for your CAS server to point to the IP address of the CAS server in Site 2. This requires the DNS records to take affect, so it can take some time to happen. Internally it'll be almost instantaneous, but external access may take 24 hours to be fully redirected.
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