We have a customer that wants to do a flip make their DR site (Site A) the active site for their already installed Exchange 2010 infrastructure. Until their new DR site comes online, they will use HQ (Site B) for Exchange DR.
Currently, they have a DAG that stretches across both sites (so not problems there.) My big concern is the CAS part. They have a Windows NLB with 2 CAS/HUB servers in Site B. I will deploy a Kemp NLB in Site A with 2 CAS/HUB servers behind it. (One of those servers already exists and I will add the other.)
They use 2 namespaces for access -- webmail.domain.com (points to Site B) and webmail2.domain.com (points to Site A).
For the switchover, I plan to (right now, I'm not worried about the order):
1. change the external and internal DNS records and switch IPs to webmail=site A and webmail2=site B
2. do the same for MX records
3. Move all DBs to DAG members in Site A
4. Use set-clientaccessarray command in each site to switch the names. Make sure the right one is applied to each DB
5. Use EMC to flip the internal/external URLs for OWA, ECP, ActiveSync, OAB
Anything I'm forgetting?