File Share Witness for Exchange 2010 in a remote Site

Posted on 2013-05-14
Last Modified: 2013-06-03
We will be installing our first Exchange 2010 SP3 server soon. We have 3 Sites all connected by high speed 10GB links. It really can be considered one big Site. Not sure why its separated other than they are different locations. We are considering collapsing our Prod Site and DR Site into one Site because we have the bandwidth. Other than the fact that the VM's are in different locations, they may as well be in the same datacenter with a 10GB link. We have redundancy also in case the 10GB link goes down. I was going to put one mailbox server and 1 CAS server in the Prod Site. 1 Mailbox server and 1 CAS server in the DR Site but have mailboxes on both. Its kind of a DR/Prod Site. The FSW will go on a server (non-exchange) in another Site. The reasoning is if our Prod Site loses power, the mailboxes should fail over to our DR/Prod Site and we will still have quorum because the servers in the DR/Prod Site can access the FSW. My only concern is I have never had a FSW in a different Site than the Exchange server and if this is allowed by Exchange.
Question by:shadowtuck
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Expert Comment

ID: 39164380
You only need FSW if you haven an even count of DAG-members.

Author Comment

ID: 39164472
Well, that is what I have. I said 1 MB server in Prod and 1 MB server in DR/Prod Site. They are both members in DAG of course for replication. That is even so I need a FSW.

Expert Comment

ID: 39164547
If the connection between the DAG nodes will be broken your DAG will work on the site where the DAG member will have access to the FSW.
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Author Comment

ID: 39164569
So, is it OK to have the FSW in another Site different from the remaining DAG member? That was my original question. I just didn't know if a FSW server had to be in the same Site as the DAG member.

Accepted Solution

amaexchange earned 250 total points
ID: 39164586
FSW must only be reachable. But note that when your Prod site has no connection to the other two sides DAG service will not work there.
LVL 63

Expert Comment

by:Simon Butler (Sembee)
ID: 39164623
You wouldn't normally have the FSW out of site.
When the link fails between the sites, then you are likely to have a failure of your DAG.
If you have locations that are physically seperate then they should be in their own AD site, with their own Exchange platform, RPC CAS array etc.

The only time you don't put the FSW in the same site is when the DAG is crossing sites, when it is impossible to have the FSW in both locations. For that scenario you should have instructions on how to do a data centre failure recovery.


Author Comment

ID: 39164744
Well, if you think about it, there is no other place to put the FSW. It cannot go in either datacenter because a power fail in either datacenter will take the DAG down as we lose quorum. It has to go off site in a third datacenter.

As for multiple Sites, if two locations are physically apart, it doesn't mean they have to be separate Sites especially with a 10GB link between them and a 15MB backup link. For all intent and purpose, they can be considered in the same datacenter. We want to leverage our second Site dubbed the DR/Prod Site by putting mailboxes on it and treat it as one big Site. I can't see any down side with Exchange doing it this way. My only concern was support for the FSW in a different Site than the DAG member and if I would be allowed to create it that way. Other concern I just thought of was using DAC mode for the DAG. With SP1, DAC mode is supported in a DAG with only two members but not sure if you need different Sites for this to work.

I have a test environment with 2 CAS and 2 MB servers and a FSW all in the same Site. It let me configure DAC for the DAG without issues so I am assuming its ok to do it this way.

Author Comment

ID: 39165770
amaexchange, we realize that. One of the prequisites to doing it this way it is fast links and redundancy in the links which we have. Typically I would not do it this way. I would set up MB servers in Prod and have everyone use them and have a passive MB server in DR site to use as failover but this place is unique with a 10GB link and we want to leverage that bandwidth and the remote location and at the same time, reduce the amount of servers needed for both Prod use and DR if needed.

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