Hello all

I am running a 5 node Exchange 2013 sp1 CU8 DAG. The DAG spans two AD sites. Both sites contain active databases.  ADsite1 contains 3 nodes, and ADsite2 contains 2 nodes. My question is what site should i place the FSW in? Also if i place the FSW in ADsite2 (2 nodes) in the event i lose the network link, would the DAG still maintain quorum and would the databases in ADsite2 remain mounted?

tha

Honestly it doesn't matter where you place the File Share witness.  Both sites are going to need a file share witness (1 is going to be the primary in the site where the active manager lives and the second is going to be an alternate in the other site).  If you lose connectivity between the two sites, the site with 3 nodes will be the only site that has quorum (3 out 5 nodes up) and will become primary for all the databases.  ADsite2 will shut itself down since it will not have quorum (only 2 out of nodes up which is less than the majority (51%) required).  Once connectivity is restored the Database copies should autoresume, and eventually catch up.  Once they catch up, then you should be able to move the DB's you want in ADsite2 back to that site.  

If you want an automatic failover to occur then you will need an even number of dag nodes in each site, and a 3rd site to place the file share witness.

Thank you for the reply. I'm a bit confused why i would need to have a FSW in both sites? is this just a recommendation if so why? currently ADsite2 has the FSW. If the link goes down between the sites, will the FSW be used in ADsite2 making 3 votes ?

Thank you

You do not need a second (alternate) file share witness. The only advantage it can give you is a slightly easier Restore-DatabaseAvailabilityGroup command should you need to run it. I recommend not specifying it at all.

If you have equal numbers of servers, whichever site can reach the FSW specified by DAG.WitnessServer is going to keep quorum and mount all databases. The other site will dismount all databases. It does not matter where the Active Manager / group owner is before this happens.

In your case, you do not have equal numbers of servers. The site with 3 servers will have a quorum (3 of 5) and mount all databases. The other site will dismount all databases. If the site with 3 servers fails, the other site will not have quorum (2 of 5) and neither site will mount databases until you use Stop and Restore-DatabaseAvailabilityGroup. The FSW is not used.

You should put the FSW in your site with more servers. This is because if you have a failed server in your primary site, you end up in the "equal numbers of servers" case.

• Marked as answer by skipster 10 hours 33 minutes ago

I would add the alternate fileshare witness when you are in the beginning stages of your migration, this way you can test and document failover procedures in the event you need them in the future.

You do not need a second (alternate) file share witness. The only advantage it can give you is a slightly easier Restore-DatabaseAvailabilityGroup command should you need to run it. I recommend not specifying it at all.

If you have equal numbers of servers, whichever site can reach the FSW specified by DAG.WitnessServer is going to keep quorum and mount all databases. The other site will dismount all databases. It does not matter where the Active Manager / group owner is before this happens.

In your case, you do not have equal numbers of servers. The site with 3 servers will have a quorum (3 of 5) and mount all databases. The other site will dismount all databases. If the site with 3 servers fails, the other site will not have quorum (2 of 5) and neither site will mount databases until you use Stop and Restore-DatabaseAvailabilityGroup. The FSW is not used.

You should put the FSW in your site with more servers. This is because if you have a failed server in your primary site, you end up in the "equal numbers of servers" case.

Bingo. I never specified the Alternate Witness in the 2010 days when I had cross site DAGs. Didn't see the point. Since you can set it on the fly when you switchover, I never saw the need.