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Balancing load between DC's

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  • Balancing load between DC's


    I currently have 2 domain controllers.

    dc1 ->
    dc2 -> (I've recently installed this)

    Both of these DC's are in the same site when viewing sites and services.

    When users logon in the morning, dc1 gets hammered. lsass consumes 80-100% CPU whilst dc2 sits there doing nothing.

    I've checked to make sure there are no weightings/priority set within DNS (thryre default) and i've also checked to make sure round robin is enabled on both servers (which it is).

    From what i've read, when you add a secondary domain controller it should automatically start to service clients - assuming it is in the same site and dns round robin is on. You can also fiddle with priority/weighting to direct clients to particular server but 'out of the box' dns should balance the load to a degree.

    Looking at my dhcp scopes, all the clients are given dc1 as their primary dns server.

    So, one way I thought to balance the load is to split the dhcp scopes so that half get dc1 and the other half get dc2 as their primary dns servers.

    Am I right in thinking that a client will use the DC it has as its primary dns server to logon with? IE if a client queries its dns server and says "who can I authenticate with" - will the dns server respond by saying "well, your already on my server so use me" or will it use round robin between the DC's specified in your site to spread the load?

    If the dns server says to the client "well your already on my server so use me to logon with" - then splitting the dhcp scopes would resolve my problem?

    Am I approaching this right? Does anyone else have a suggestion on how to measure load on DC's, or how to ensure it is split evenly etc?


  • #2
    Re: Balancing load between DC's

    I take it you've run DCDIAG and NETDIAG and see nothing odd there?

    Have you tried making DC2 the primary DNS for everyone and does the traffic then move to DC2? If it doesn't then splitting the DHCP scope as suggested won't buy you anything. And if it does, wouldn't that indicate a problem with your DNS config?

    Here's a post on how to adjust LdapSrvWeight and LdapSrvPriority for a DC in the registry:

    Never experimented with this and I keep trying to find someone that will.

    Don't know if it is a good fit for you as it appears, with this little bit of info and a whole lot of assumptions, your problem lies elsewhere.


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    • #3
      Re: Balancing load between DC's

      Another thing to check is that the second DC is setup as a Global Catalog server.

      This should help with the authentication in the morning as it will be able to service logons.


      • #4
        Re: Balancing load between DC's

        What is the DC's hardware spec and how many users do you have ?
        Guy Teverovsky
        "Smith & Wesson - the original point and click interface"


        • #5
          Re: Balancing load between DC's


          Thanks for your replies.

          We had 2 new agents pushed to DC1 (MOM and IBM Director agents) and after disabling them, lsass on DC1 has dropped down to normal levels (about 30-40% of cpu)

          After viewing logon attempts on both DC1 and DC2 we could see that both were authenticating clients (> nltest /serveromainControllerName /LOGON_QUERY) so I started looking at other possibilities. DC1 still takes the brunt but it is balancing the load to some extent.

          I went on a bit of a tangent looking at dhcp scopes and dns etc thinking that was the problem.

          It didnt make sense that changing the scopes around would fix that (thanks for highliting that rval).

          If the load isnt split evenly we might look at using weight/priority but for now it looks good.

          Cheers fellas!