none
Best practice for disabling Replication on DAG Network....

    Question

  • I am looking for guidance on when to have "Replication Enabled" on the DAG network. I have the following environment:

    2 Physical sites

    3 member DAG:

    2 Dag Members in Site A

    1 DAG Member (stretched) in site B

    The two DAG members in site A has two nics, a MAPI nic and a "Replication Network" nic. I currently have Replication disabled on the MAPI nic. I have Replication enabled on the "Replication Network". Is this correct so far?

    For the single DAG member in Site B (the server wtih a single nic), should I have Replication enabled or disabled? Does it matter in a single nic DAG member?

    One last question: I have read that it is recommended that all DAG members have the same number of nics. So if my Site B DAG member has only one nic, should I remove the "Replication Network" on the two DAG members in site A, so they both have only 1 NIC as well (and MAPI and Replication would happen on same nic)?

    Thanks for the help.



    Tuesday, March 06, 2012 6:23 PM

Answers

  • No worries Rich!

    I'd push for the two NIC scenario as that allows a better HA design in the primary DC.  Yes the traffic may all flow over the same VPN to the second site, but I really want to see separate MAPI and REPL interfaces to address the lossy failover scenario I mentioned. 

    For the VPN/WAN link I've seen many permutations.  Even some larger orgs have a single WAN pipe between locations. 


    Cheers, Rhoderick

    Wednesday, March 07, 2012 5:12 PM

All replies

  • 2 Physical sites

    3 member DAG:

    2 Dag Members in Site A

    1 DAG Member (stretched) in site B

    ---------------

    MAPI -Nic

    Replication - Nic

    --------------

    Its good to have 2 Nics on all the servers

    if one fails , it will switch over to the other Nic

    No matter if you replication enabled or disabled

    For Example - your Mapi Nic won't be used for Replication Currently

    But if your replication NIC fails due to some reason . MAPI NIC will be used for replication as well

    ----

    So its always recommended to have 2 NICs on all DAG members

    Dedicating a Replication Network having Replication Disabled on MAPI networks

    Give good Replication Health. Also it doesn;t disturbs the MAPI giving good productivity


    Satheshwaran Manoharan | Exchange 2003/2007/2010 | Blog:http://www.careexchange.in | Please mark it as an answer if it really helps you

    Tuesday, March 06, 2012 7:15 PM
  • One last question: I have read that it is recommended that all DAG members have the same number of nics. .

    Hi Rich,

    Actually, "Each DAG member must have the same number of networks. For example, if you plan on using a single network adapter in one DAG member, then all members of the DAG must also use a single network adapter. "

    For more information, please see Network Requirements topic:

    Planning for High Availability and Site Resilience

    http://technet.microsoft.com/en-us/library/dd638104.aspx#NR

    I would also suggest you have two NICs for each DAG member.

     

    Please remember to mark the replies as answers if they help and unmark them if they provide no help. If you have feedback for TechNet Subscriber Support, contact tnmff@microsoft.com.


    Frank Wang

    TechNet Community Support

    Wednesday, March 07, 2012 8:04 AM
  • Wow, I guess I totally missed that requirement when I implemented DAG. Thank you. The interesting thing is that I have been running DAG since July of 2011 with very few issues, EXCEPT that I have been getting Event ID 1135 a couple times a day on my offsite DAG member (the one with only one nic). I started a thread about that here

    http://social.technet.microsoft.com/Forums/en-US/exchange2010/thread/e9b28365-7174-478b-b09f-5a1997d547a1

    I have only one Point to Point VPN between site A and site B. Of course all MAPI traffic flows over this point to point, as well as all DAG traffic. Would it be a best practice to try to stand up another VPN between the two sites just for DAG traffic, or would the replication traffic be better just to route over my existing VPN? BTW, I am using TMG 2010 SP2 at both ends of my Point to Point.

    So, it looks like if I have a single nic DAG members, the "Replication" setting does not matter, since both mapi and dag traffic flow through the same nic?


    Wednesday, March 07, 2012 1:28 PM
  • Create a Persistence route for the Replication Network

    Have Correct NIC bindings , 1. MAPI , 2. Replication

    Its always good to have MAPI and Replication in different LANs to have High availability

    Cause have one LAN is always a Single point of Failure when Comes to LAN

    If you run a Cluster Validation Report - it would clearly Explain you.


    Satheshwaran Manoharan | Exchange 2003/2007/2010 | Blog:http://www.careexchange.in | Please mark it as an answer if it really helps you

    Wednesday, March 07, 2012 2:53 PM
  • So, it looks like if I have a single nic DAG members, the "Replication" setting does not matter, since both mapi and dag traffic flow through the same nic?


    If a single NIC then yes, though as Frank mentioned we support that but recommend two NICs in all DAG servers (and require the same config in all members).

    Why ?

    We want to avoid a lossy failover scenario when the attempt copy last log process happens.  If the only NIC is dead then there is no way to get the remaining transactions off the failed DAG member.  If we have the second NIC (Replication) and the MAPI were to fail then there is a mechanism to copy the last log over and the world is a happier place :) 

    I'd also suggest that you look into teaming to make the MAPI network even more available (if possible).  Please read Tim's blog here:

    http://blogs.technet.com/b/timmcmic/archive/2010/05/30/network-port-design-and-exchange-2010-database-availability-groups.aspx 

    Also make sure that the DAG networks have been collapsed, and all the other support criteria in Frank's article have been taken care of.


    Cheers, Rhoderick

    Wednesday, March 07, 2012 4:45 PM
  • So, it looks like if I have a single nic DAG members, the "Replication" setting does not matter, since both mapi and dag traffic flow through the same nic?


    If a single NIC then yes, though as Frank mentioned we support that but recommend two NICs in all DAG servers (and require the same config in all members).

    Why ?

    We want to avoid a lossy failover scenario when the attempt copy last log process happens.  If the only NIC is dead then there is no way to get the remaining transactions off the failed DAG member.  If we have the second NIC (Replication) and the MAPI were to fail then there is a mechanism to copy the last log over and the world is a happier place :) 

    I'd also suggest that you look into teaming to make the MAPI network even more available (if possible).  Please read Tim's blog here:

    http://blogs.technet.com/b/timmcmic/archive/2010/05/30/network-port-design-and-exchange-2010-database-availability-groups.aspx 

    Also make sure that the DAG networks have been collapsed, and all the other support criteria in Frank's article have been taken care of.


    Cheers, Rhoderick

    Thank you for this guidance, this is very helpful.

    I would like to get some advice on the VPN setup for DAG. Since I have only a single VPN currently between Site A and Site B, does it make sense to have 2 nics on the DAG members? I know the VPN becomes a single point of failure, but am wondering how people are actually implementing this guidance for the recommendation of 2 nics per DAG member. From my reading, it seems like the (stretched) DAG feature of exchange 2010 is very, very popular (and it has worked very well in my environfment), just curious if people in the SMB segment are doing multiple VPNs to their remote datacenters.

    Wednesday, March 07, 2012 5:03 PM
  • No worries Rich!

    I'd push for the two NIC scenario as that allows a better HA design in the primary DC.  Yes the traffic may all flow over the same VPN to the second site, but I really want to see separate MAPI and REPL interfaces to address the lossy failover scenario I mentioned. 

    For the VPN/WAN link I've seen many permutations.  Even some larger orgs have a single WAN pipe between locations. 


    Cheers, Rhoderick

    Wednesday, March 07, 2012 5:12 PM
  • It is recommended that all DAG members have equal number of NIC cards otherwise the configuration may malfunction.

    The replication network is the heartbeat of the cluster and not for production environment if one system fails the other system starts to replace the failed computer in the network.

    The second network is for production environment,all  clients and other computers are connect through this network and replication should be disabled here from the EMC to reduce the traffic in the network.

    It is possible to run the DAG using  a single nic but it is not recommended


    Thursday, March 08, 2012 7:30 AM
  • It is recommended that all DAG members have equal number of NIC cards otherwise the configuration may malfunction.

    Please note that Frank already mentioned this, and it is not a recommendation it is a requirement. 

    Maybe it would be helpful to use the word "must", i.e. all nodes MUST have the same number of NICS. 

    Does that make it clear Devaraj ?


    Cheers, Rhoderick

    Thursday, March 08, 2012 2:41 PM