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Creating a CAS Array on 2 Exchange Servers with DAG

Posted on 2011-09-09
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I've been looking around at articles as there are plenty about but I have also read about some conflicting information about NLB, Vmware, and Clustering.

As this is a Live system I thought I'd best check!

Currently:

Exch1 - All roles. Active copy of MBDB01
Exch2 - All roles. Passive copy of MBD01 + empty MDB02 (not used for now)

Both on VMWare with 1 Production NIC and one Replication NIC

Both configured in a DAG.

MX: remote.domain.com
DNS: remote, autodiscover pointing to Exch1

How should I proceed in creating a CAS array?

End result I would like to achieve:

1. Load balancing between the 2 servers - not important but if it can be achieved without Hardware LB, great.
2. Automatic failover for ALL services (Mailbox and Client Access) should one server go down
3. Failback? Or is this manual?



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Question by:hongedit
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Tony J earned 668 total points
ID: 36509542
Simply you cannot create a CAS array without putting in two new Exchange servers.

DAGs and CAS arrays cannot exist on the same server. DAGs use aspects of Windows Clustering and this cannot run on the same server as NLB.

As you have VMware, have you considered creating a single new CAS server with an FT lockstep pair? Fault Tolerance creates a secondary copy of the virtual machine on another host. If the primary fails, the secondary carries on without any failure and in the background (if possible) creates another lockstep pair on another host.

Or just use HA - if the host that the CAS server is on dies, it'll reboot the VM on another host.

All of which is predicated on having a 'full' version of VMware, not the free one.
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by:hongedit
ID: 36509584
Hi Tony

Thanks, much clearer.

I have the full VMWare but no shared storage at the moment (it's coming) so HA/FT is not possible right now.

I created the DAG partially for "experience" and partially for mailbox redundancy against failures.

I think I'll wait til the SAN is here (was going to use VSA but the space limitations are far too great right now) and do the single CAS on FT.

Thanks
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by:Akhater
Akhater earned 1332 total points
ID: 36509601
I know this question is closed but, with no offense, the answer is wrong

Do not confuse DAG and CAS High availability,

DAG are to provide redundancy for your mailbox database, for CAS high availability you will need to create a CAS array

now the issue you have is that your MBX and CAS are on the same servers so that rules out windows NLB it cannot be done together with clustering but that leaves you with many options.

 1. you create a CAS array for you CAS server and you use a hardware load balancer to balance your CAS servers
2. You create a CAS array and you use DNS round robin for load balancing the traffic across your cas servers, the obvious draw back of this solution is that the failover is not automatic, in the case of a server failure the dns will not know that the server is down and will still send requests to it so you will need to go and manually edit the DNS to delete the record of the failing server
3. you create a cas array and you point the cas array name to the DAG ip, this will give you automatic failover but no load balancing
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by:Tony J
ID: 36509614
Which part of the answer is wrong?
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by:Akhater
ID: 36509632
>Simply you cannot create a CAS array without putting in two new Exchange servers.

DAGs and CAS arrays cannot exist on the same server. DAGs use aspects of Windows Clustering and this cannot run on the same server as NLB.<

This part, a CAS array has nothing to do with windows load balancing. a CAS array can be created on the 2 servers with any of the above stated scenarios

The fact that windows clustering and windows NLB does't coexist doesn't mean the OP can't create a CAS array or use a dedicated load balancer to balance his cas server without adding 2 new exchange servers
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by:hongedit
ID: 36509641
Load Balancing is not a requirement, simply a nice to have feature. Automatic Failover is much more important to me.

Hardware LB is NOT an option.

So where does that now leave me? Point 3, "Create a CAS Array but point it to the DAG IP"?

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by:Tony J
ID: 36509643
Ok fair comment - however I read it as how to install a CAS array on the existing setup without additional hardware, so not wrong - just differences of interpretation.
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by:Tony J
ID: 36509652
I would go with what I originally said. VMware do now support HA for Exchange (including MBX servers). They have a support statement somewhere on their website from about a year ago.

I would use what you've already paid for and let VMware do the HA. No added complexity or licensing.

You could create an additional CAS (only) server if you're nervous about HA'ing a DAG partner.
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by:Tony J
ID: 36509661
That is - CAS (only) _virtual_ server...
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by:hongedit
ID: 36509674
SAN is about 6-7 months away yet I think, but for the sake of my own knowledge:

With my current setup, I could create a CAS array on my existing 2 Exchange Servers that both hold all roles, but instead of using Windows NLB I could just point it to the DAG IP to achieve automatic failover, at the expense of no Load Balancing.

Is this correct?
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by:Akhater
ID: 36509683
@Tony1044 I have been here long enough to know you and I do know you are a valuable addition to the community, believe me I am not trying to put any pun on you and I am sorry if you got my comment wrongly

 just for info starting SP1 exchange MBX DAG on virtual high available environment is now supported on both VMWare and HyperV

I have no idea myself about vmware or FTlockstep so I cannot talk about this part but I would go for the option of pointing to the cluster IP since I would need no extra servers to install or anything.


again I am a total ignorant if VMWare so take my decision with a grain of salt
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by:Akhater
ID: 36509690
>>With my current setup, I could create a CAS array on my existing 2 Exchange Servers that both hold all roles, but instead of using Windows NLB I could just point it to the DAG IP to achieve automatic failover, at the expense of no Load Balancing.<<

that is exactly what I would have done if load balancing is not curcial
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by:hongedit
ID: 36509709
Cool.

So how do create the CAS Array :D All the guides  out there dont vary much from the "default" scenario

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by:hongedit
ID: 36509711
Running SP1 btw!
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by:Tony J
ID: 36509723
@Akhater - no offence was taken at all. No 'peeved' tone was intended in my response. I value a two way flow of information.

FYI I'm not disagreeing with any point you made, just clarifying how I read the initial question.
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by:Akhater
ID: 36509724
New-ClientAccessArray -name CAS01 -FQDN CAS01.domain.local -site "ADSiteName"

that's it nothing more to do, just make sure to change the RpcClientAccessServer to CAS01.domain.local

get-mailboxdatabase | set-mailboxdatabase -RpcClientAccessServer CAS01.domain.local
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by:Akhater
ID: 36509729
@Tony1044 thank you
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by:hongedit
ID: 36509737
>New-ClientAccessArray -name CAS01 -FQDN CAS01.domain.local -site "ADSiteName"

that's it nothing more to do, just make sure to change the RpcClientAccessServer to CAS01.domain.local

get-mailboxdatabase | set-mailboxdatabase -RpcClientAccessServer CAS01.domain.local<

Sorry I'm a bit dumb.

Do I need to run this on both servers or just any one of them?

Also, how does this  affect external (Outlook Anywhere) connected clients?

I assume I need to create a DNS entry: CAS01.domain.local > DAG IP?
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by:Akhater
ID: 36512659
>>Sorry I'm a bit dumb.

Not at all we are all here to learn

>>Do I need to run this on both servers or just any one of them?
Any of them


>>Also, how does this  affect external (Outlook Anywhere) connected clients?
It will affect all your outlook clients, outlook is using the new CAS array as rpc server

>>I assume I need to create a DNS entry: CAS01.domain.local > DAG IP?
perfectly right


Just one thing you should be aware of, if you have clients already configured with outlook these will not switch (unfortunately) to the cas array name automatically
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by:hongedit
ID: 36512743
Thanks.

Do I need to set any external DNS in reference to the new CAS Array name? Or is that resolved through the RPC Proxy settings in Outlook?

When you say Outlook Clients will not automatically switch, do you mean I need to reconfigure them as follows:

Instead of having ExchangeServer1.domain.local in the SERVER field, I should have CasArray1.domain.local instead?
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by:hongedit
ID: 36512748
If I create a CAS Array (casarray1.domain.local) will clients still be able to connect to ExchangeServer1 directly, if I have not reconfigured them yet?
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by:hongedit
ID: 36512754
I ask as I have some remote users which I may not be able to get to them all immediately
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by:Akhater
Akhater earned 1332 total points
ID: 36513090
>>Do I need to set any external DNS in reference to the new CAS Array name? Or is that resolved through the RPC Proxy settings in Outlook?

No external DNS record needed for the CAS array name


>>When you say Outlook Clients will not automatically switch, do you mean I need to reconfigure them as follows:
Instead of having ExchangeServer1.domain.local in the SERVER field, I should have CasArray1.domain.local instead?

Perfectly right

If I create a CAS Array (casarray1.domain.local) will clients still be able to connect to ExchangeServer1 directly, if I have not reconfigured them yet?

Yes no problem

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by:hongedit
ID: 36522764
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