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What should client see when CAS server fails

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What should client see when CAS server fails - 9.Nov.2011 8:27:25 AM   
cdooer

 

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Joined: 23.Feb.2005
From: Canada
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Hello. We're about to roll out Exchange 2010, and I was wondering if someone could shed some light on what my clients should experience when one of the CAS servers goes offline. We are using hardware load balancers, and during our testing the failover seems to happen ok, but the Outlook client see's a 'trying to connect' message for 2-3 minutes until it finally connects to the second CAS server. The load balancer see's the downed CAS server immediatley (we disable the NIC on it), and I was wondering if the lag that is experienced is due to the new session being setup on the second CAS server. We're running our clients in cached mode, so it isn't a big deal. If they were to try and send an email at the exact time of the failure, it simply sits in their outbox until the second CAS server is online.

So, is this 2-3 minute delay normal behaviour with hardware load balancers?
Post #: 1
RE: What should client see when CAS server fails - 9.Nov.2011 2:02:49 PM   
cdooer

 

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Joined: 23.Feb.2005
From: Canada
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I guess nobody's witnessed a CAS server failure from the client side while using hardware load balancers?

(in reply to cdooer)
Post #: 2
RE: What should client see when CAS server fails - 9.Nov.2011 5:54:34 PM   
svoller

 

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Joined: 26.Dec.2010
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We have been testing this in the lab, I dont think we are seeing the same lag you are but it will depend on how you have configured the LB.

What type of persistence options have you taken ?

(in reply to cdooer)
Post #: 3
RE: What should client see when CAS server fails - 9.Nov.2011 9:28:59 PM   
ermanishchawla

 

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do you have configured CAS array ?? or just simply you connected two CAS to hardware load balancer.. Just configure CAS array and your MAPI switchover will be near seamless !!

(in reply to cdooer)
Post #: 4
RE: What should client see when CAS server fails - 10.Nov.2011 9:24:24 AM   
cdooer

 

Posts: 6
Joined: 23.Feb.2005
From: Canada
Status: offline
We're using SourceIP persistence. I'm assuming its a CAS array, our Exchange guys set it up. I'm responsible for the NLB's. They are A10. So, the failover should be seamless. Looks like I'll have to keep digging.

(in reply to ermanishchawla)
Post #: 5
RE: What should client see when CAS server fails - 10.Nov.2011 11:43:04 AM   
ermanishchawla

 

Posts: 125
Joined: 12.Jul.2011
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I guess you got confused between load balancing concept and cas array.

CAS array can be implemented using windows NLB or using hardware load balancer. But Can you just verify whether your cas array is registered to mailbox database

or
simply follow the link  to check whether you have done like this
http://blogs.technet.com/b/ucedsg/archive/2009/12/06/how-to-setup-an-exchange-2010-cas-array-to-load-balance-mapi.aspx

(in reply to cdooer)
Post #: 6
RE: What should client see when CAS server fails - 10.Nov.2011 12:19:19 PM   
cdooer

 

Posts: 6
Joined: 23.Feb.2005
From: Canada
Status: offline
We do indeed have a CAS array, which contains 3 CAS servers. The NLB's are A10 AX1000's. I've followed the deployment guide provided by the vendor, and am load balancing SMTP, RPC and HTTPS. I am not, however load balancing the auto-discover function. Does anyone know if auto-discover is used in detecting a failed server?

Like I mentioned earlier, the failover does seem to happen, but from a clients perspective there is a 1-3 minute disconnect, and we were expecting it to happen seamlessly.

(in reply to ermanishchawla)
Post #: 7

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