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CAS Resiliency design RRS feed

  • Question

  • Hi All,

    Currently planning the following Exchange 2010 design.

    2 physical sites, one in the US and one in Europe.

    Each site should be configured as following:

    1 Mailbox server

    1 CAS server

    1 DAG on a virtual machine at another location a few miles down the road.

    The mailbox server and the DAG will provide resiliency for mailboxes.  I need to provide resiliency for the CAS servers so would like the two CAs servers  to work in some kind of failover mode. When both servers are up and running I would like the US based users to connect to the CAS server in the US and Europe based users to connect to the CAS server in the UK. When either server is down, I would like all users to failover  to the good CAS server. I am assuming then that I need a load balancing solution that will use geogrphic location as its primary weighting and availability as its secondary.

    From what I have read, It seems I cannot use a typical CAS array configuration as the CAS servers will be in different AD sites. I am open to suggestions be it a software or hardware load balancing solution. I have read a lot of good things about the Kemp technologies products but am unable to find enough information there to make an informed decision. 

    please help

    regards

    Monday, May 2, 2011 11:16 PM

Answers

  • CAS Array is defined within an AD site.  So if you have 2 AD sites you will need a CAS Array in each site.

    You may be able to use a Hardware NLB such as Citrix Netscaler.  If using WNLB, then you're defined as above unless you have a strecthed AD site, which I don't recommend.

    Sukh

    • Proposed as answer by Human Being_001 Tuesday, May 3, 2011 7:27 AM
    • Marked as answer by Gavin-Zhang Thursday, May 5, 2011 5:48 AM
    Monday, May 2, 2011 11:45 PM

All replies

  • CAS Array is defined within an AD site.  So if you have 2 AD sites you will need a CAS Array in each site.

    You may be able to use a Hardware NLB such as Citrix Netscaler.  If using WNLB, then you're defined as above unless you have a strecthed AD site, which I don't recommend.

    Sukh

    • Proposed as answer by Human Being_001 Tuesday, May 3, 2011 7:27 AM
    • Marked as answer by Gavin-Zhang Thursday, May 5, 2011 5:48 AM
    Monday, May 2, 2011 11:45 PM
  • Thanks , I kinda figured that  with the CAS array needing to being in one site. The problem with that is following.  If for example, the US site is down (disaster of some kind) , the users should be able to take their laptop home, connect with their outlook anywhere client to a CAS server and connect to the copy of their email at the DAG on the Europe site. Having two or more CAS servers in an array will not let that happen. 

     

    However,  I am not sure how a HLB will help.  Don't know enough about them I guess. Although I could configure the individual CAS servers in each site with the virtual IP address of a hardware load solution, would a HLB be able to decide when to connect outlook to the mailbox server if available and to the DAG if not?

    Da Soca

    Monday, May 16, 2011 1:47 AM
  • 1. If your DAG members includes the US and Euro servers.  Should US site fail, the US users DB should be activated on the Euro site.  When users go home and use OA, they will use the CAS servers at the Euro site as the US db would not be activated on the Euro DAG member.  Maybe you should consider settting up your DAG this way if infrastucture permits.

    2. HLB (depending how configured) will choose the appropiate CAS server Outlook will connect to.  This is what the HLB will do.  HLB will not decide on which database to connect to in such, this depends on which DAG member it's activated on.

    See below to help you understand HLB a little more.

    http://www.msexchange.org/articles_tutorials/exchange-server-2010/high-availability-recovery/load-balancing-exchange-2010-client-access-servers-using-hardware-load-balancer-solution-part2.html

    Sukh

    Monday, May 16, 2011 1:10 PM
  • So here are my concerns with what you are saying

     

    to 1. If the US site fails, the only way a user will connect to the European CAS server is if the CAS servers are in an array otherwise the US client will still be trying to connect to the US CAS sever. But like I said before, because these will be different AD sites, I cannot have an array that spans these sites.  And that is my problem with the HLB.  Does a HLB change the client endpointattribute it delivers to the US client when it becomes aware that the US CAS server is unavailable?

     

    Also, can anyone point me to a HLB vendor that operates in the same price class as the Kemp products? based on the scenario I have here, I guess I need to be looking for a HLB solution that does all the Layer 4 - 7 load balancing as well as having a weighting metric based on geographical location

    Wednesday, May 18, 2011 1:53 AM
  • Any more help on this please?
    Tuesday, May 24, 2011 11:06 PM
  • Try loadbalancer.org.

    Very similar to Kemp.

    We went with WNLB in the end due to tight budgets but their pre-sales were very helpful and on the ball.

    Wednesday, May 25, 2011 10:28 AM