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Exchange 2010 DAG

Posted on 2010-08-23
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Last Modified: 2012-05-10
I have an exchagne 2010 server and want to build a second one on my older server, and create a "DAG" , after creating this how will my users connect to outlook, will it need to be adjusted to the cluster IP/Name? also, i would prefer users connecting to my more powerful server, will this be an option. If someone could help me understand this id appreciate it.

thanks,
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Question by:zingab
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by:gustav25
ID: 33501463
Hi,

a DAG is only a cluster of your mailbox databases. Your Outlook clients will connect to your Client Access server and not to your mailbox servers.
A DAG is active-passive, which means that only one database is in use. You as an administrator can set which database is the active one.

Regards,
gustav
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Author Comment

by:zingab
ID: 33501481
so when building my second exchange server what roles will i need, guess i am not understand what Dag is actually dong.
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by:gustav25
ID: 33501521
Which roles do you have on your first server?
A DAG simply transports the logs of your mailbox database to the other database server and applies it.
So you have a backup if one of your database servers fails.

But the mailbox servers are not reponsible for the connections of outlook. There you need the server role Client Access.
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Author Comment

by:zingab
ID: 33501530
all roles are on one exchange server, its a small environment
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by:Busbar
ID: 33501541
In Exchange 2010 clients are not connecting to the mailbox role anymore , it rather connects to the RPC service installed on the Exchange 2010 server.
so when installing the second role you will need a mailbox server role
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by:gustav25
ID: 33501572
If you have the Client Access role on the same server as your mailbox server and the mailbox server crashes, a DAG won´t keep your environment running.
You have to set up an alternate Client Access server for the connections of outlook, webapp etc. and you also need another Hub transport server to deliver your mails.
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Author Comment

by:zingab
ID: 33501778
so creating a dag is useless with having all roles on the same server?
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by:Busbar
ID: 33501824
slightly disagree, you can have DAG with all of the server roles configured but you will have to use external hardware load balancer to load balance the traffic and provide HA for the CAS/HUB server role.
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Expert Comment

by:gustav25
ID: 33501924
No it isn´t useless, because you have a funcitonal copy of your database if one server fails.
But you have to make the other roles high available, too.
If you don´t care about your CAS and HUB then you don´t need a DAG.
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Author Comment

by:zingab
ID: 33502075
to clarify- so i dont need a dag, but i can just make a fucntion copy of my databse? how would i go about that?
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by:gustav25
ID: 33502116
No sorry, you missunderstood what I said.
A DAG copies the database and its contents for you.
This is not done manually.
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Author Comment

by:zingab
ID: 33502170
Besides automatica failover, what else am i losing with having all the roles on one server if i create a dag?
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by:gustav25
ID: 33502210
If your client access role is not present in case of failure, no client can connect to your mailboxes. WebApp won´t work anymore and also Active Sync.
You won´t be able to send and receive Emails when your Hub server is missing.

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Author Comment

by:zingab
ID: 33503604
would i be able to install all roles on the second server then manually move to them upone failure?
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by:gustav25
ID: 33508123
Quite a good question, I haven´t tried this so far.
I think this works, but somewhere deep inside my head I remeber a MS knowledge base article with some limitations to the CAS placement. But right now I can´t find this article.

But keep in mind you have to be careful with the configuration of your server roles.
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Author Comment

by:zingab
ID: 33511876
if you happen to locate some info on this shoot it my way, i cannot i have searched...
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by:gustav25
ID: 33518393
I´m sorry, I also have to look this up in technet and this issue is far to complex to explain here. So I am out for the moment.

Bye
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Accepted Solution

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endital1097 earned 500 total points
ID: 33558750
i just want to make sure i understand what we are looking for here
you would like to utilize the new DAG feature with exchange 2010, but it is for a small company so you would like to have all three roles (CAS, HUB, and MBX) all running on both servers.

this is a possiblity with only one area of concern
as you know all mailboxes are connected using RPC Client Access on the CAS
which CAS is used by the Outlook client is controlled by the RpcClientAccessServer value on the mailbox database

what you can do is create a client access array with your two exchange 2010 servers (ex. mail.contoso.com)
create a DNS A record for this CAS array
then you can update your databases to use this CAS array (Set-Mailboxdatbase
DBName -RpcClientAccessServer mail.contoso.com)
then you need to determine a type of load balancing mechanism to control client connections, which you only have two options
1. hardware load balancer
2. round robin dns

since this is a small shop, you most likely want to look at round robin dns
yes, there will be connection attempts made to the downed server in the event of an outage. set the TTL value for your CAS array records to a small value, and delete the downed server entry during an outage.

this doesn't give you the maximum up-time solution, but it is a cost effective alternative that will give you high availability

since you mentioned this is for a small company
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Author Comment

by:zingab
ID: 33577943
Endital, thanks for the reply, is this the only way you see this as possible?
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by:endital1097
ID: 33578011
unfortunately for smaller companies, yes, exchange 2010 is limiting for ha
i forgot to mention earlier that you cannot use Windows NLB with Windows Failover Clustering (used by DAG) and that's why it isn't listed as option 3

there is always virtualization, but once again there is cost
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Author Closing Comment

by:zingab
ID: 33580877
ty for your time!
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