Hi all,

I have two exchange 2013 servers in two locations (one in each location). I configured a DAG which contain both servers.
Each Server has an active mailbox database with the user from the location.

Is an file share witness directory necessary on each location? At the moment I have only one file share witness directory on location A.
But what will happen if both exchange server are online and working fine but the connection between the locations is lost? How does exchange know which databases must be online when there no connection between the two locations?

What are your recommendations or what is best practices in this scenario?

Thanks for help

Best
Malte

You should specify an alternate witness directory for the node in the second site.  It will facilitate the failover process should you ever have to failover to that site due to the loss of the first site.

Hi

 Best pratice is fle share withness on Domain Controller,and add alternate witness folder another DC or file server,important point is the witness directory always up and accessible.

Hi,

thanks for the answer. I configure the a fsw directory on each location. 

But what will happen after the connection between the two locations is available again?

As the connection was down between the locations both exchange server have the same databases online because as they had to assume that the other exchange server was unreachable.

Best Malte

Hi again,

When the connection is avaible again between two location replicate the data's on file withness folders for all DB's.(DB changes i mean)

 

Hi

 Best pratice is fle share withness on Domain Controller,and add alternate witness folder another DC or file server,important point is the witness directory always up and accessible.

You should not use a DC for a file share witness.  The reason is you need ot make the Exchange Trusted Subsystem a Local Administrator on which ever server you use as the File Share Witness.  

There is no local administrator group on a Domain Controller, so your only option at that point is to make the Exchange Trusted Subsystem a Domain Administrator.  

I don't know about anyone else, but for me that is something I don't want to do.  

Best Practice is to use a File Server for the Witness Directory.

Hi,

thanks for the answer. I configure the a fsw directory on each location. 

But what will happen after the connection between the two locations is available again?

As the connection was down between the locations both exchange server have the same databases online because as they had to assume that the other exchange server was unreachable.

Best Malte

If the connection between the 2 sites fails, then the site A with the defined file share witness will still be active (it will have 2 quorum votes) but site b will not activate the alt. file share witness automatically (that's a manual process) so it will shutdown.

Since you're dag spreads 2 sites you also want to make sure you enable DAC mode. 

https://technet.microsoft.com/en-us/library/dd979790%28v=exchg.150%29.aspx

http://blogs.technet.com/b/rmilne/archive/2013/12/04/dac-and-should-i-enable-dac-for-a-dag-in-a-single-ad-site.aspx

http://exchangeserverpro.com/datacenter-activation-coordination-mode/

 

I also suggest you take a look at this article it has some great information about DAGS.

http://exchangeserverpro.com/exchange-server-2013-database-availability-groups/

Hi,

thanks for this good information. I have one more question. This is the configuration:

Location A:
EX01
Database A active
Database B passiv
primary FSW directory

Location B:
EX02
Database B active
Database A passiv 
secondary FSW directory

Now the connection between the locations is lost. What will happen on both servers with an enable DAC Mode ?

Which Database is on which server online?

Thanks for help

BR Malte

Hi,

thanks for this good information. I have one more question. This is the configuration:

Location A:
EX01
Database A active
Database B passiv
primary FSW directory

Location B:
EX02
Database B active
Database A passiv 
secondary FSW directory

Now the connection between the locations is lost. What will happen on both servers with an enable DAC Mode ?

Which Database is on which server online?

Thanks for help

BR Malte

Everything should be active on EX01 in site A. Since only 1 FSW can be the primary at a time, Site A will be the only site that can achieve Quorum Majority (will have 2 votes out of 3 while Site B only has 1 vote (EX02)).

Hi

 Users connect their DB without any problem(i mean users on Database B connect from location B,users on Database A connect from location A )then when the connection comes up,replicates DB changes between your 2 MBX Exchange.

Hi

 Users connect their DB without any problem(i mean users on Database B connect from location B,users on Database A connect from location A )then when the connection comes up,replicates DB changes between your 2 MBX Exchange.

Not how quorum works in this scenario. Quorum can only be achieved if you have a majority of votes (> 51%). If you don't have the majority of votes, no DAG for you.

SO here's what should happen.  If you lose connectivity between the 2 sites the Exchange Servers in both sites check to see where quorum is.  EX01 in Site A will see that it has it's vote and the FSW's vote so that gives Site A 66% of the votes, it will also see that it cannot communicate with EX02 in Site A and mount DB2.  Meanwhile in Site B, EX02 will see that it has lost communication with BOTH the FSW in Site A and EX01 in Site A and it will not have Quroum and will dismount it's database and shutdown it's cluster service until communication is restored.  

Once communication is restored, EX02 should add itself back to the DAG, replication should pick up where it left off, and once it catches up, you should be able to mount db02 on EX02 again.

The only way DB02 will stay mounted on EX02 during a communication failure between both sites is if you setup a 3rd site and put the FSW in that third site and communication does not fail between Site 3 and Site 2.