This guide simply explains in a very easy way, all the technologies and procedures that you need to know to perform Exchange 2010 data center switch over, recovering DAG member or stretching DAG between sites.
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3. Data Center Switch Over
3.1 Terminate the primary data center
- DAG Members in the primary data center must be marked as stopped. Stopped is the status of Active manager that prevents database copies to be mounted on them, and will exclude them from DACP voting. This can be done on the primary and the secondary sites :
o On the Primary side :
o If the mailbox servers in the primary are operational and there is a functioning DC in the primary site, use
Stop-DatabaseAvailabilityGroup -Identity DAG1 -ActiveDirectorySite NYC
o If the mailbox servers in the primary site are not operational but there is domain controller in the primary site, use this command for each primary MBX servers:
Stop-DatabaseAvailabilityGroup -Identity DAG1 -MailboxServer E14EX3 –ConfigurationOnly
o If no DC nor mailbox servers are available in the parent side, then make sure that mailbox servers are shutdown always.
o If the primary mailbox server are online, make sure the cluster service is set to Disabled or do it yourself.
o On the Secondary side :
o We need to tell the secondary site which servers are available during the switch over. This can be done by using the Stop-DatabaseAvailabilityGroup command with the ConfigurationOnly.
- UM Servers:
If any Unified Messaging servers are in use in the failed datacenter, they must be disabled to prevent call routing to the failed datacenter. You can disable a Unified Messaging server by using the Disable-UMServer cmdlet (for example, Disable-UMServer UM01).
Alternatively, if you are using a Voice over IP (VoIP) gateway, you can also remove the Unified Messaging server entries from the VoIP gateway, or change the DNS records for the failed servers to point to the IP address of the Unified Messaging servers in the second datacenter if your VoIP gateway is configured to route calls using DNS.
3.2 Activating Mailbox Servers
- When the primary datacenter is down, the mailbox servers in the secondary site, will try to take ownership of the cluster group and will try to bring the primary Witness server online for couple of time before timing out and failing. This is when the cluster as a whole goes down because of majority issues. Database copies on primary datacenter mailbox servers appears as (Service Shutdown), where database copies on secondary datacenter mailbox servers appear as (Disconnected and Healthy)
- The Cluster service must be stopped on each DAG member in the primary datacenter. This can be one of two:
- If the Primary data center is down, then for sure objective completed
- If the primary mailbox servers are online, make sure cluster service is stopped and the service is marked as disabled
- Running Restore-DatabaseAvailabilityGroup which will do two things :
- Evict Stopped DAG members from cluster
- Create alternative witness share if not created previously on the DAG level
Restore-DatabaseAvailabilityGroup -Identity DAG1 -ActiveDirectorySite LON – AlternateWitnessServer EXHUB1 -AlternateWitnessDirectory D:\DAG1
You may need to run the command couple of time until the primary mailbox servers are evicted from the cluster.
Note: the restore command can fail, just wait 5 minutes and run it again. Also you can make sure that the command is being executed on the right domain controller by running:
Set-ADServerSettings –PreferredServer <Domain Controller in Failover Datacenter>
- Always and at any time, if you want to force the cluster model to refresh (i.e if you open the cluster console from the secondary mailbox server, alternative witness share should appear after you entered the Restore-DatabaseAvailabilityGroup command, if it didn’t reflect in the cluster console, just type Set-DatabaseAvailabilityGroup –Identity DAGName)
- You should make sure the Witness server and directory are up. Never lose them and avoid restarting them. Make sure Exchange Trusted Subsystem is member of the local administrator group on the Witness server and create a firewall rule on the Witness server if necessary to allow all traffic from the mailbox server to the Witness Server.
- At this moment, the secondary mailbox server(s) will try to assume the ownership of the cluster group and trying to get the secondary DAG IP online and will keep trying to bring the alternative Witness share online.
- Use Get-DatabaseAvailabilityGroup cmdlet to make sure the Stopped servers are those mailbox servers in the primary site while started servers are those in the secondary site only.
- If databases in the secondary site don’t mount automatically, remember to remove any activation blocks on the server level (Set-MailboxServer) or on the database level (Suspend Activation).
- If still databases didn’t mount correctly, use this command:
Move-ActiveMailboxDatabase –Server FQDNofaServerinPrimarySite –ActivateOnServer FQDNofaServerinDRSite
This command contains many Skip switches that can be handy.This is very important step as it is like taking ownership of those databases. You can also use :
Move-ActiveMailboxDatabase DatabaseName –ActivateOnServer FQDNofaServerinDRSite
- We need to choose whether to remove the database copies existing in the primary site to allow log truncation or not. If we choose so, reseeding will be necessary once you fail back to the primary data center.
- Outlook Office clients will act as per the following :
- If the primary CAS servers are online, CAS servers in the primary site will issue a silent redirect message to outlook users. Outlook users will see a message that they need to restart their outlook.
- If the primary CAS servers are online, you can change the DNS name for the outlook anywhere name or just force autodiscover to work by repairing outlook profile
- OWA clients will do the following :
- If the primary CAS servers are online, silent redirection will happen since both OWA virtual directories has Integrated Authenticated on them
- If the primary CAS servers are offline, DNS name for OWA primary should point to secondary and that’s it.
- If you restarted mailbox servers in the secondary site and/or the Witness server, the DAC bit will be sit to 0 and databases will be shown as Dismounted. If you try to mount them , an error that the replication services on the primary mailbox servers are not online. You may find a problem locating the Active manager also especially if you typed: Get-DatabaseAvailabilityGroup –Identity DAGName – Status. The solution will be forcing the DAC bit to be 1 by running the Start-DatabaseAvabilibityGroup –Server (Secondary Mailbox Servers) even if they are already started.