none
Exchange 2010 DAG with just 2 servers RRS feed

  • Question

  • Hi all,

     

    I have the following scencario that I need some assistance;

    - 60 email users (70% Mobile Users, probably going to use OWA)

    - Need to setup HA between just 2 servers (In other words, need to setup Hub,CAS & Mailbox roles on these 2 servers)

    - Need to understand how can I configure HA for these roles Hub, CAS & Mailbox on these 2 servers?

     

    With this requirements & design, can I achieve the basic failover should one of the server dies and what's the duration of the downtime am I looking at?

     

    Any feedback/advice will be much appreciate.

    Cheers,

     

    Monday, July 26, 2010 12:00 AM

Answers

  • So with Exch 2010, ALL client connectivity goes through the CAS role so it is probably the most important role.  When using more than one CAS server, you would create a CAS array.  When using a HLB, the FQDN of the CAS array is pointed to the HLB.  All clients will use the CAS array FQDN for connectivity.  The HLB is configured in such a way that it "monitors" the CAS servers.  If it detects that one of the servers is unavailable, then it will not continue to send connections to that CAS server.  Once the offline CAS server is back online, it will be added into the mix automatically by the HLB.  I say HLB, but software based load balancers are also supported be Microsoft (F5 and Citrix).  See the link to see all supported load balancers...

    http://technet.microsoft.com/en-us/office/ocs/cc843611.aspx

     


    Tim Harrington - Catapult Systems - http://HowDoUC.blogspot.com
    Monday, July 26, 2010 1:57 AM

All replies

  • If using 2 servers and want HA for all roles, then you will set up DAG for the MB, and a CAS Array load balanced by a hardware load balancer for the CAS role (DAG uses Windows Failover clustering and CAS without a HLB would use Windows network loadbalancing, the two services can't be installed on the same server).  The HUB role is HA be default, include both HUB servers in the outbound Send connector.  With this set up, you should have no more than 30 seconds of downtime during a failover.  The best blog I have found that explains all options is this one:

    http://www.shudnow.net/2010/03/17/exchange-2010-rtm-high-availability-load-balancing-options/

     


    Tim Harrington - Catapult Systems - http://HowDoUC.blogspot.com
    Monday, July 26, 2010 12:19 AM
  • Thank you sir for your revert, if I am not going to use HLB for my CAS Array, in other words, I would only require failover on my mailbox servers, would it still work?

    Sorry if I get your explanation wrong.

    Monday, July 26, 2010 12:33 AM
  • Let's say you have 2 servers with all roles installed.  The HUB, CAS, and MB roles are required for Exchange operation.  If you did not create a CAS array and load balance them, then if you lost a server, you would be able to failover your MB databases just fine, but overall operation would not work because you would not have a properly configured CAS role.  Let me know if you need more explanation.  The link above does a good job of explaining the different options for HA of all roles.
    Tim Harrington - Catapult Systems - http://HowDoUC.blogspot.com
    Monday, July 26, 2010 12:39 AM
  • Thanks for the prompt revert, I can understand the rationale for having a HLB, another quick question with regards on how Clients can access via the CAS?

    Is it going be achieve thru the loadbalancer, in other words, the load balancer will be able to know if either one of the server (CAS) is down?

    Correct me if I am wrong, I need to understand how clients access via the CAS in this design (2 x servers)

     

    Cheers,

    Monday, July 26, 2010 1:48 AM
  • So with Exch 2010, ALL client connectivity goes through the CAS role so it is probably the most important role.  When using more than one CAS server, you would create a CAS array.  When using a HLB, the FQDN of the CAS array is pointed to the HLB.  All clients will use the CAS array FQDN for connectivity.  The HLB is configured in such a way that it "monitors" the CAS servers.  If it detects that one of the servers is unavailable, then it will not continue to send connections to that CAS server.  Once the offline CAS server is back online, it will be added into the mix automatically by the HLB.  I say HLB, but software based load balancers are also supported be Microsoft (F5 and Citrix).  See the link to see all supported load balancers...

    http://technet.microsoft.com/en-us/office/ocs/cc843611.aspx

     


    Tim Harrington - Catapult Systems - http://HowDoUC.blogspot.com
    Monday, July 26, 2010 1:57 AM
  • Note that mapi client access to public folders do not go through the CAS , but still go directly to the pf server.
    Monday, July 26, 2010 2:15 AM
    Moderator