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DAG with load balancer

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DAG with load balancer - 9.Dec.2011 1:35:15 AM   
MichaelCaditz

 

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Can I have a hardware load balancer connected to two boxes, each containing CAS, HUB, and MBX roles, and each being a node in a DAG?

If one box contains an active copy of a mailbox database and the other box contains the passive copy, then what happens if the load balancer sends a client access request to the box with the passive copy?
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RE: DAG with load balancer - 9.Dec.2011 2:27:13 AM   
rahulrao9

 

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Can I have a hardware load balancer connected to two boxes, each containing CAS, HUB, and MBX roles, and each being a node in a DAG?

Yes you may have hardware load balancer connected to two boxes running CAS/HUB/MBX roles. Using windows NLB for CAS high availability and using DAG which uses components of Windows failover cluster together are not recommended where all the roles are installed on same box.
Hardware load balancer can be used for the CAS roles for client access requests, MBX role will make use of Windows failover cluster manager and HUB transport role will load balance among itself as they have their built in logic to load balance themselves.

If one box contains an active copy of a mailbox database and the other box contains the passive copy, then what happens if the load balancer sends a client access request to the box with the passive copy?
All incoming client request will be processed by the hardware load balancer and they will directed to your CAS role and not the mailbox role. In exchange 2010 all the client requests such as OWA, active sync EWS including outlook are handled by CAS role. MBX role is just for saving the mails sent by the users. Hence Client access is not directed to the mailbox role.CAS role will be handling the user end requests.
For your reference and understanding
http://technet.microsoft.com/en-us/library/bb124915.aspx

Hope this clears!!!!

(in reply to MichaelCaditz)
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RE: DAG with load balancer - 9.Dec.2011 2:46:44 AM   
rahulrao9

 

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To make things clear
DAG do not require Load balancer because when you configure DAG it by default makes use of components of windows failover clustering,where as you can increase the high availailty of CAS role by including a hardware or software load balancer.
Windows NLB is inbuilt feature of windows server 2008 SP2 or R2 and the same cannot be used along with the DAG(where MBX and CAS role are installed on same server).

(in reply to rahulrao9)
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RE: DAG with load balancer - 9.Dec.2011 3:35:27 AM   
rahulrao9

 

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Also refer these articles listed below - Intresting read

http://technet.microsoft.com/en-us/library/ff625247.aspx

http://technet.microsoft.com/en-us/library/ee332317.aspx

(in reply to rahulrao9)
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RE: DAG with load balancer - 9.Dec.2011 3:40:27 AM   
rahulrao9

 

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Also refer these articles listed below - Intresting read

http://technet.microsoft.com/en-us/library/ff625247.aspx

http://technet.microsoft.com/en-us/library/ee332317.aspx

(in reply to rahulrao9)
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RE: DAG with load balancer - 9.Dec.2011 11:38:01 AM   
MichaelCaditz

 

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Thank you.

Do I have this correct, then?

If one of my boxes with CAS and HUB and active MBX database fails, then the hardware load balancer sends client requests to the CAS on the other box; and DAG failover makes the passive MBX database on the other box active; and the client doesn't know anything happened?

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RE: DAG with load balancer - 12.Dec.2011 2:15:16 AM   
rahulrao9

 

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Yes if 1 of the CAS/HUB/MBX servers fails it will failover to another server.At client end their might be a slight disconnect for a short period of time until Database become active on another server.It will not be because of CAS failover ,but because of MBX database failover.
But again it all depends how you have configured.
It is recommended to keep your servers up to date with latest patch
Exchange 2010 SP2 has been released.You may try it in your lab environment and if no issues found you may try it on your Production environment.

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RE: DAG with load balancer - 25.Jan.2012 3:21:06 PM   
online_pc_support

 

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To further what people have said. If you have 2 x Exchange Servers, both with the MBX, CAS and HT roles.

Lets call these EXCHANGE01 and EXCHANGE02

Lets say that both Exchange servers hold a copy of the only mailbox database in the organization and EXCHANGE01 has this mounted.

When clients are hitting the load balancer, if the load balancer is setup to balance clients using round robin, then the first client will be directed to the CAS on EXCHANGE01, the second client to the CAS on EXCHANGE02, and the third to the CAS on EXCHANGE01 again etc.

Now if the mailbox database was to fail on EXCHANGE01, it would first be marked as failed, and because EXCHANGE02 is a member of the DAG and holds a copy of the mailbox database this would be Mounted and start serving both CAS servers.

Clients would still be hitting both CAS servers, but the back end requests would be making transactions with the Mailbox Database Copy stored on EXCHANGE02.

It is easier to think of this if have a totaly seperated Exchange environment, so you have CAS01 CAS02 MBX01 MBX02 HT01 HT02

You have just got all of these roles on 2 x Servers.

I hope this makes it easier to understand :)

Scott
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RE: DAG with load balancer - 9.Feb.2012 8:45:52 PM   
MichaelCaditz

 

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Thank you, everyone. It all makes sense, and I'm up and running in production.

I have a separate issue, though, regarding DAG architecture spanning three AD sites:

http://forums.msexchange.org/DAG_subnets/m_1800558720/tm.htm

Penny for your thoughts!

(in reply to online_pc_support)
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RE: DAG with load balancer - 22.Feb.2012 12:55:13 AM   
janejackson

 

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Of course it's possible that are CAS, HTS, MBX roles on the same server with WNLB if it doesn't need a DAG. But I think nobody would use like that. So it is required another hardware load balancer. 

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