Implementation of CAS Array

Hi, We have three exchange servers 2010 on which all the three roles (CAS/HT/MBX) are installed. This servers are in DAG and within  site only.

Now we are planning to install CAS Array in existing environment for fault tolerance of client connections.  
Can someone guide what would be the prerequisites and changes need to be done in existing organization.
sanjayambreAsked:
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Simon Butler (Sembee)Connect With a Mentor ConsultantCommented:
You should create the CAS Array now so that you can start to move clients to it.
Otherwise the only thing to worry about is that the CAS role servers must always be the same version or higher than the mailbox servers.

You would have been better of spending the money on a load balancer rather than additional Exchange licences. A load balancer is a lot better solution than WNLB.

Simon.
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jimmithakkarConnect With a Mentor Commented:
Need to use Windows NLB or hardware load balancer,

before that create CAS array

http://exchangeserverpro.com/exchange-server-2010-cas-array/
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sanjayambreAuthor Commented:
Thanks for links...Our servers are in DAG that means Failover Cluster Service  is installed.
Do NLB & FCS are supported simultaneously. If not, what is the alternative option to implement CAS Array in our environment.
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jimmithakkarCommented:
Microsoft will not recommend for using NLB and cluster in same system,

If you have around 1000 user than follow below

first need to create CAS array, let ex. acasarry.mylab.local, then create DNS record for acasarray,

like:

acasarray = A record (Primary Mail server IP)
acasarray = A record (secondary Mail server IP)

DNS server user round robin functionality and load balance b/w to IP for acasarray

# one of my client using same for 5000 user
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sanjayambreAuthor Commented:
Ok..In our current environment, CAS & MBX role installed on same server, so we can't install NLB on same server, right?
Do we need to install separate CAS servers.
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Mahesh SharmaCommented:
FCS & NLB should not be mixed, its an unsupported scenario.

If you still want to try then you can use multiple NIC's each for FCS & NLB.

Otherwise go for Hardware load balancer
Or if may use ISA/TMG for load balance & have your CAS array point to it.
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Mahesh SharmaConnect With a Mentor Commented:
http://blogs.technet.com/b/exchange/archive/2011/04/08/robert-s-rules-of-exchange-multi-role-servers.aspx


The single real limitation of the multi-role is the fact that WNLB is not supported on the same server running Windows Failover Clustering. Although Exchange 2010 administrators never have to deal with cluster.exe or any other cluster admin tools, the fact is that DAGs utilize Windows Failover Clustering services to provide a framework for the DAG, utilizing features such as the quorum model and a few other things. This means that if you have a DAG in a multi-role architecture, and you need load balancing (as all highly available solutions will need), you will be forced to purchase a hardware load balancer.
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sanjayambreAuthor Commented:
That means either we have to purchase hardware load balancer or Separate CAS server for NLB, right?
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Mahesh SharmaCommented:
Yeah, You are right.
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jimmithakkarCommented:
If you can buy hardware load balancer is good otherwise use DNS round robin, it will also work

no need to install separate CAS on other server.
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sanjayambreAuthor Commented:
Please elaborate how DNS round robin works for RPC client connections.
Does it remove requirement of NLB?
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Simon Butler (Sembee)Connect With a Mentor ConsultantCommented:
The Exchange product team do not recommend the use of WNLB for Exchange, which is a good job as it sucks. Therefore instead of purchasing additional Exchange licences, get a load balancer.

DNS does not provide any kind of redundancy, It does not remove the need for a load balanced solution unless you are prepared to make manual DNS changes.

Now for the really bad news - you should have had a CAS Array host name in Exchange from day 1. Even if you configure it now, none of the clients will start using it automatically. That means that even if you do have load balancers etc the clients will not go through them.

The only way to get the clients to use the CAS Array address is to repair the Outlook profile. That has to be done by hand - in Outlook accounts, select the account and click repair. That forces the update to happen.

Simon.
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sanjayambreAuthor Commented:
Simon, Thanks for clarification.
We  have small organization and hardware load balancer is expensive so we might choose second option to create additional CAS servers since we have additional licenses.

What else we have to consider before creating another CAS servers?
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