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Switchovers and Failovers are two distinct processes in Exchange that are performed or occur in response to an outage or failure that affects the database, server, or the entire site. They are used to protect Exchange server mailbox databases and data contained on the server. You can use Switchover and Failover to configure your mailbox server and database for site resilience and high availability.
The key difference between the two is that in Switchover, manual activation of one or more database copies is required. In Failover, the process of activating one or more database copies after failure is automatic.
What is Switchover in Microsoft Exchange Server?
A Switchover is usually performed when you want to update or upgrade your Exchange server while maintaining high availability. It is a planned or scheduled downtime or outage of the data center, server, or database. It is initiated by the IT or Exchange admin manually via cmdlet or Exchange Admin Center for scheduled maintenance. In this process, a copy of the active mailbox database is moved to another server in the Database Availability Group (DAG).
After moving the mailbox database, you can update or perform maintenance tasks on the server and then reboot with no repercussions or issues to the user’s connectivity.
Types of Switchovers
In the Exchange Server, there are three types of Switchovers:
1. Database Switchovers
In Database Switchover, an active database is switched over to another database copy or new active database copy. This can be performed across or within datacenters by using Exchange Admin Center (EAC) or Exchange Management Shell (EMS). One would usually do this to reduce the load of a particular server.
2. Server Switchovers
Like Database Switchover, Server Switchover can occur within or across the datacenter. In Server Switchover, all current active database copies are moved to one or more other servers that are members of the Database Availability Group. In this case, one can shut down the server or replace/upgrade any hardware.
3. Datacenter Switchovers
Datacenter Switchovers are performed in the event of site-level failure.
Steps to perform Switchover by using PowerShell
The steps to perform database or server Switchover by using PowerShell are as follows:
Important Note: You must be assigned the correct permissions to perform the procedure(s).
Step 1: Prepare for Switchover
Run Exchange Management Shell (EMS) as administrator and then execute the following cmdlet to list all Exchange servers in the organization.
Get-ExchangeServer | Format-Table Name, Edition, Serverrole, AdminDisplayVersion
This displays the Exchange server name, edition, server role, and the Exchange version (build number). Once you have the list of databases, you can list all the databases on all servers or individual server by using the following commands:
Get-MailboxDatabase -Status | sort Server | Format-Table Name, Server, Mounted
Get-MailboxDatabase -Status | ? {$_.server -like "EXSRV01"} | sort Name | Format-Table Name, Server, Mounted
Step 2: Perform Switchover
To perform a database or server Switchover, you can use the Move-ActiveMailboxDatabase cmdlet. It lets you move all current active mailboxes from one server to another within or across datacenters. Using the following command on EMS, you can move all the databases from Exchange server EXSRV01 to Exchange Server EXSRV02.
Move-ActiveMailboxDatabase -Server EXSRV01 -ActivateOnServer EXSRV02
Once the Switchover is complete, the Exchange server EXSRV02 hosts an active copy of the database that was on EXSRV01.
If you would like to specify which database to move, you need to specify it in the command, as given below:
Move-ActiveMailboxDatabase DB01 -ActivateOnServer EXSRV02
You may also use the following command to perform Server Switchover for EXSRV01.
Move-ActiveMailboxDatabase -Server EXSRV01
Step 3: Verify Switchover
Once the Switchover is performed, you can verify if the Switchover was successful by using the following command:
Get-MailboxDatabase -Status | sort Server | Format-Table Name, Server, Mounted
The command output will display all the databases that are active on the Exchange server EXSRV02.
Steps to perform Switchover by using Exchange Admin Center
The steps to perform Server Switchover by using Exchange Admin Center (EAC) are as follows:
Step 1: In the EAC, navigate to Servers > servers.
Step 2: Choose the Mailbox server that you want to Switchover.
Step 3: Choose Server Switchover in the details pane.
Step 4: Perform one of the following steps on the Server Switchover page:
- Accept the default setting of Automatically choose a target server and click save.
- Click Use the specified server as the target for Switchover, click Browse to choose a Mailbox server. Then click
NOTE: If you choose the first option, the system selects the best Mailbox server automatically for each Database Switchover.
Step 5: After the Switchover is completed, click on close to exit.
What is Failover in Microsoft Exchange Server?
Unlike Switchover, a Failover is activated automatically in response to a database, server, or site failure. A Failover occurs at the database, server, or datacenter level during an unexpected outage due to failure of the database, server, or datacenter. It helps ensure high availability by automatic recovery, where active mailbox database copies are moved to another server in DAG.
Types of Failovers
Like Switchovers, there are three types of Failovers in Microsoft Exchange Server:
1. Database Failovers
A Database Failover comes into action when the active database on the server deactivates or no more remains in an active state.
2. Server Failovers
A server Failover occurs when the MAPI network is down and becomes unserviceable or cluster service fails to contact the other remaining DAG members.
3. Datacenter Failovers
A Datacenter Failover occurs in the event of a site failure.
How does Failover work?
A Database Failover comes into action when database failure is detected by the Exchange Information Service.
- The Active Manager on the server that hosts a failed database detects the failure and initiates a request for a database copy from another server in DAG.
- The server responds with the status, after which Primary Active Manager (PAM) starts the process of moving the best copy of the active database.
- The PAM also updates the new location where the database is mounted in a cluster database and informs the Active Manager on the target server.
- The Active Manager then requests Exchange Replication Service to copy the logs from the primary server.
- Finally, Exchange Replication Service copies the logs from the old server, and Exchange Information Service mounts the new copy of the active database.
Although failures are automatically handled by the server, in some failures, Failovers may not work and require the administrator to initiate recovery. This could be an issue with the secondary site, with the operating system, hardware, storage, connectivity, or other problems.
Switchovers and Failovers in Microsoft Exchange Server: Final thoughts
Microsoft Exchange is designed to handle both Failovers and Switchovers that protect a mailbox database and data contained in it. They ensure site resilience and high availability to avoid downtime during server maintenance or database, server, or database failure. While Switchover is a planned or scheduled outage performed manually by the Exchange admins for maintenance tasks, Failover comes into play when an unexpected outage is detected due to failure of the database, server, or datacenter. However, Switchover and Failover may not work in some scenarios that can lead to downtime and data loss. In such cases, you can rely on an Exchange recovery tool, such as Stellar Repair for Exchange, to restore mailboxes and email services during an outage or failure of database, server, or datacenter in the least possible time, while using less effort from the administration side.
You may also like to read:
- How to manage log files in Exchange server: Step-by-step guide
- Exchange Server disaster recovery: Step-by-step planning
- Exchange Server maintenance checklist: Avoid downtime, prevent disaster
- Configured Exchange for high availability? You can still face an extended outage
- Need to recover failed member of a Database Availability Group?
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