CAS Design Question

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DG1212

I have 4 Exchange 2010 servers in my environment. One CAS/HT, and mailbox in AD site1 and one CAS/HT and mailbox in AD site2. I know that CAS arrays can't span AD sites, so what it the best way to configure a DR configuration? Would it be better to change the DNS record to point the the CAS/HT in Site2 or to change RpcClientAccessServer switch to point to the alternate CAS?

Are there any other options that are more automatic?
 
S

Sembee [MVP]

Personally I wouldn't want anything automatic to change the configuration. I like the fact that I have to do something manual, even if this is to just change the DNS record, as it means that the traffic is under my control.

If you have the second server connected by a WAN, then you are looking at the most common problem being the WAN failure. Once the two sites are isolated, what happens then?
Are you running a DAG behind the CAS array?

The way I have the smaller sites setup, where I am not using a separate load balancer is a short TTL on the DNS. In the event of having to switch to the other site, then I make the change in DNS. That ensures that nothing is changed because the WAN has dropped.
I work on the basis that if I have lost the other site for some reason bigger than a WAN drop, then I am going to have bigger problems than email to worry about, and if I am simply rebooting the server, I don't want all of the clients switching to a server in another site and flooding the WAN link.

Simon.

Simon Butler, Exchange MVP
Blog | Exchange Resources
 
D

DG1212

Yes, I have a DAG setup between the two sites. Would I need to change the DNS record as well as RpcClientAccessServer switch to point to the CAS in Site2?
 
S

Sembee [MVP]

That depends on what scenario you are planning for.

If the CAS server is still up and the mailbox server is what has failed, then nothing would have to be changed, because the clients are still pointing to the same CAS server - remember that it is CAS that handled the connection to the mailbox server.

However if you are planning for the CAS server to fail, then you would almost certainly have to change both the RPC Client Access array value on the database to the CAS array value in the second site (as the CAS array host is AD site specific) and the DNS to point to the other server. That should mean that Outlook will connect to the second site and have its server value corrected to the second CAS array. I don't think that changing the DNS is enough - but I haven't tested that for a while and it isn't in my notes from when I did.

Manual intervention, but under your control.

Simon.

Simon Butler, Exchange MVP
Blog | Exchange Resources
 
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