I currently have an exchange 2010 server that hosts all three roles CAS,HUB, Mailbox Database.. EDGE Role is handled by postini.

I want to move the CAS,Hub role to a dedicated server and leave the current server to just work on the database role.

What is the process to make this happen with zero downtime.. is this even possible?

so we ran into a couple of snags.. so want to run a new idea by you.

our Current Mailbox/Cas/Hub is running on windows 2008 r2 standard.. so it cant support dag's.. so here is the new plan.

  1. Building New Mailbox Server (MB1)
  2. Build New secondary Mailbox Server (MB2)
  3. COnfigure new DB using Dags on MB1 and MB2
  4. Online move all users to new DB's on MB1
  5. Remove Mailbox Role from old Cas/Hub/Mailbox Server
  6. user old Cas/hub/mailbox server to only run CAS/Hub

if we do this.. it should be doable.. but anyone who has done this is there any downtime?


1 Answer 1


With one mailbox server, a zero-downtime migration will not be possible.

The closest you can get would be:

  1. Install and configure new CAS server.
  2. Create a new DNS A record for your CAS servers with the IP of your new CAS server. (For example, if your CAS servers are called mail1 and mail2, make a new DNS name called cas.)
  3. Create a new CAS array in PowerShell using this new DNS name for Fqdn.
  4. Use Set-Mailbox to change the RpcClientAccessServer of your database to this new DNS name. (This will cause your clients to attempt to connect to the CAS server via the new DNS name you created.)
  5. Wait for all clients to move to new CAS server.
  6. Uninstall CAS roles from MBX server. This will cause an outage.

The advantage of creating a CAS array instead of just reconfiguring to use the new CAS server is that if you need additional CAS servers in the future for performance or availability reasons adding a new CAS server and a load balancer can be a zero-downtime operation.

If you want zero-downtime, then you will need another mailbox server and a DAG:

  1. Set up new mailbox server with no other roles.
  2. Set up DAG to replicate all of your databases to the new server.
  3. Failover all databases to the new server.
  4. Follow the instructions above.
  • what DNS Records are you referring to? the autodiscovery record?
    – Greg
    Jun 10, 2013 at 19:30
  • In a high-availability or load balanced scenario, you would create a DNS name for your CAS servers that points to your load balancer. What does Get-ClientAccessArray say your fqdn and members are?
    – longneck
    Jun 10, 2013 at 19:36
  • i get nothing back.. i dont think i have a cas array. currently i have only 1 cas.
    – Greg
    Jun 10, 2013 at 19:56
  • see my edit above.
    – longneck
    Jun 10, 2013 at 20:34
  • Thanks for all the help.. out of curiously how long of an outage does the uninstall of the cas role cause? and what is the cause of the said outage?
    – Greg
    Jun 10, 2013 at 20:44

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