• Exchange 2010 needs to be able to failover to a secondary datacenter, if the primary datacenter loses power or experiences some kind of catastrophic failure.
• Four VM mailbox servers (A, B, C, D)
• Two VM CAS servers (Cas-A, Cas-B)
• Two hardware network load balancers (NLB1, NLB2)
• All MBX servers, CAS servers and NLBs are in one AD site.
• One DC, NLB2, Cas-B and MBX server “D” are all running in the secondary datacenter.
• Secondary datacenter is connected to the primary datacenter via a 1GB fiber connection.
• Currently running a DAG that consists of one active DB on each MBX server and three passive DBs on each MBX server. The three passive DBs consist of one copy each of the other three servers.
• File Share Witness (FSW) is currently set to Cas-A in the primary datacenter, per what I understand to be the best practice of putting your FSW in the physical location that contains the greatest number of MBX servers.
• Additionally, the IT Director has mandated that the FSW remain in the primary datacenter due to the likelihood of the link between the
• I can set the FSW to CAS-B in the secondary datacenter. If I do this and the primary datacenter goes down, then nothing else needs to be done. The DBs in the DAG will failover to server D and both NLB2 and Cas-B will handle all the client traffic.
• However, if I set the FSW to the secondary datacenter and the connection between the two goes down (disaster, fiber cut, etc), then we lose the ability to connect to the DBs in the primary datacenter.
• I know I can simply change the FSW to Cas-A and it will work. However, if I do this and the secondary datacenter comes back up, then I am going to wind up with the system in a “split-brain” scenario.
• So…I can set an Alternate FSW. But if I do that, then it is my understanding that I need to enable the Datacenter Activation Coordination (DAC) mode, so that when the primary datacenter comes back up, I don’t wind up with a “split-brain” scenario. I would do that with this PS command:
oup –Identity DAG1 –DatacenterActivationMode DagOnly
Okay…so the steps I have been able to piece together for using the Alternate Witness Server in case the primary datacenter goes down are as follows. Please correct me if they’re wrong:
1. Stop the clustering service on Server D
2. Run this PS command from Server D:
a. Stop-DatabaseAvailabilityGroup -Identity DAG1 -Mailboxserver ServerA –Configurationonly
b. Stop-DatabaseAvailabilityGroup -Identity DAG1 -Mailboxserver ServerB –Configurationonly
c. Stop-DatabaseAvailabilityGroup -Identity DAG1 -Mailboxserver ServerC -Configurationonly
3. Run this PS command from Server D:
a. Restore-DatabaseAvailabilityGroup -Identity DAG1 -Mailboxserver ServerD –Configurationonly
4. Mount the databases on Server D.
At this point, all DBs should be running on Server D.
To fail back to the primary datacenter, I will need to:
1. Bring up Servers A, B, and C.
2. Connect to one of the servers.
3. Run these PS commands:
a. Move-ActiveMailboxDatabase ExchDB1 -ActivateOnServer ServerA -MountDialOverride: GoodAvailability
b. Move-ActiveMailboxDatabase ExchDB2 -ActivateOnServer ServerB -MountDialOverride: GoodAvailability
c. Move-ActiveMailboxDatabase ExchDB3 -ActivateOnServer ServerC -MountDialOverride: GoodAvailability
4. Restart the databases on the primary servers (A, B, C).
5. Disable the Activation bit on the databases on Server D:
a. Suspend-MailboxDatabaseCopy -Identity ExchDB1\ServerA -ActivationOnly
b. Suspend-MailboxDatabaseCopy -Identity ExchDB2\ServerB -ActivationOnly
c. Suspend-MailboxDatabaseCopy -Identity ExchDB3\ServerC -ActivationOnly
So what do you folks think? Am I overthinking it or did I get it right?