To answer this question, first you have to know that the difference between CAS servers in Exchange 2007 and Exchange 2010 is that Exchange 2007 CAS servers only process IMAP, POP, Web and Web Services. With Exchange 2010, CAS servers will also handle MAPI traffic. So, besides balancing ports 80, 443 etc. you also need to balance ports 135 (TCP) and 6005-65535 (TCP/UDP) for MAPI RPC ports. Note that you can also use static ports when required, consult kb270836 (it’s an old article, but still valid).
Now on to the new CAS array. CAS array are built on top of load balanced configurations – being hard- or software based. Since the role of CAS servers is becoming more important because it handles all client traffic, it is important to create redundancy at this level. Here’s when Exchange 2010’s CAS array comes into play. With CAS arrays you can create one “virtual CAS server” where you can point all mailbox servers.
The process of creating a CAS array is as follows:
- Install CAS servers;
- Set up load balancing, either using NLB or hardware. Don’t forget to add the MAPI RPC ports (see above);
- Create a DNS record (A) for the virtual IP address of the CAS array, e.g. myarray.contoso.com;
- Create the CAS array object using the New-ClientAccessArray cmdlet, e.g.New-ClientAccessArray –Name “My Array” –Fqdn “myarray.contoso.com”
Note that there’s a limit of 1 CAS array per site and you can define the site for the CAS array using the Site parameter when required.
(image by Henrik Walter)
The final step depends on the overall installation sequence and if any Mailbox servers existed before the creation of the CAS array, you may need to correct Mailbox servers configuration. These will probably still point to the individual CAS servers, which we can correct using the Set-MailboxDatabase cmdlet like this:
Set-MailboxDatabase Mbx1 -RpcClientAccessServer “myarray.contoso.com”
Note that when a CAS array is present, Mailbox servers will be configured to use that instead of the first CAS server at installation time.
So the answer to the question is CAS Arrays are built on load balanced configurations, load balancing configuration (software or hardware) is still required. For more background information on Client Access Servers in Exchange 2010, consult this TechNet topic.