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I have two 2003 DCs.  Should BOTH of them be Global Catalog servers as well?

Posted on 2008-06-10
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Last Modified: 2011-09-20
Just curious, because when one of them goes down, no one can connect to Exchange or anything......I'm wondering if making them both Global Catalog servers would fix this issue, as I believe that5's what having two DCs is all about in the first place!  Good idea?  Bad idea?  If I make them both GC servers, do I have to do anything on the Exchange side so that Exchange is aware of both?
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Question by:tenover
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by:rakeshmiglani
ID: 21752361
no changes are required on exchange.
it will pickup the GC/DC automatically
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by:SowelaIT
ID: 21752482
This really depends on your domain set up.  If this is a single domain then you really only need one GC.  I'm told that unless you need a second GC you really should not put multiple GC's on your domain controllers due to increased replication traffic which could place a large overhead on those servers.

As for the Exchange problems:
The suggested ratio is 1 Global Catalog for every 4 Exchange 2003 servers. Now, if you have a small number of users on Exchange and a few well powered servers, you can put it on each DC.  The best and only true way to test if this setup will work for you is to make a copy of your GC on your other DC and watch the processor and memory on each server, as well as watch for slow logins, Exchange issues,  and other issues caused by domain and GC latency (such as problems in the Universal Group Membership lookup areas, etc.).
And if you find that it puts too much of a strain on the domain, just put it on your most reliable DC and cross your fingers.
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by:Jeff Perry
ID: 21752484
What version of exchange server are you running?

I have noticed that when my GC is rebooted that users loose connectivity to our exchange 2007. I am considering putting GC back on our other DC to see if it prevents this as well.
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by:SowelaIT
ID: 21752517
Also, when moving the GC, remember to check into FSMO roles best practices.

http://www.windowsdevcenter.com/pub/a/windows/2004/06/15/fsmo.html
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Author Comment

by:tenover
ID: 21752591
I'm not moving the GC.  I wanted to know if adding the GC role to my second DC would resolve the issue of Exchange 2003 not being available when the DC/GC is down or being rebooted.  I'm running Exchange 2003 Enterprise with about 150 mailboxes.  Single domain at a single site.  All servers are Dell Poweredges bought in the past 3 years.
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by:SowelaIT
ID: 21752781
To be honest, I have run dual GC's on our domain.  We were having problems with one and instead of running out at midnight to reboot the dead machine I just duplicated it and rebooted in the morning.    

The good thing about running two GC's is that it the computers needing access to the GC may be sped up due to the round robin questioning of the GC.  

Personally I would go for it but I would try it out on a weekend or some time when traffic is not at the greatest.
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by:DrDave242
ID: 21753065
I'd say go for it.  With a single domain and single site, replication traffic won't be much of an issue, if at all; it's not like you're replicating over a slow WAN link.  Making that second DC a GC will give you redundancy in case the other one goes down, although if your DC is going down more than once in a blue moon, there's a problem that you'll really want to look into.
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Author Comment

by:tenover
ID: 21753239
That's what I thought.  And no, the DC's have never gone down, but occasionally I'll need to reboot or something.  Should just making both GCs allow access to Exchange if one is down, or is it ALSO dependent on the FSMO roles?
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by:DrDave242
ID: 21753330
During installation, Exchange needs to contact the Schema Master in order to extend the AD schema, but I don't believe it's dependent on any of the FSMO roles during normal operation (although it needs to sync time with the PDC Emulator like everything else in the domain).
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by:raptorjb007
ID: 21753377
It is best practice to have at least two GC's configured in any domain. Any additional GC's depend on your environment, ie remote sites with no redundant wan link, overloaded DC's etc etc.

My option is that you should definitely configure the second DC as a GC as the additional load in a smaller environment is negligible.
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SowelaIT earned 2000 total points
ID: 21753494
The five FMSO roles (PDC Emulator, RID Master, Infrastructure Master, Domain Naming Master, and Schema Master) are not neccessary for Exchange to do it's job.  If they are off line for a few minutes for a reboot, you may not be able to do things like add computers or install Exchange, but your email should work just fine.
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