In today’s world, email is one of the most critical communication channels for businesses. Microsoft Exchange Server is a popular email server and collaboration solution used by businesses of all sizes worldwide. To ensure high availability and reliability of the email service, Microsoft introduced the concept of Database Availability Groups (DAGs) in Exchange Server 2010. This article provides an introduction to Exchange DAG and a step-by-step configuration guide.
What is a Database Availability Group (DAG)?
A Database Availability Group (DAG) is a high availability and disaster recovery solution in Exchange Server. It is a group of up to 16 Exchange Server Mailbox servers that host a set of databases and replicate them to provide automatic database-level recovery from failures that affect individual servers or databases.
By creating a DAG, you can ensure that your email service remains available even if one or more servers or databases fail. DAGs use continuous replication technology to replicate the mailbox databases to multiple servers, allowing you to maintain multiple copies of the mailbox databases in different locations.
Before creating a DAG, there are several requirements that must be met:
- At least two Exchange servers are required to create a DAG.
- The servers must be running the same version of Exchange Server, and the same service pack level.
- The servers must be members of the same Active Directory domain.
- Each server in the DAG must have a unique name and IP address.
- The mailbox database copies must be created on different physical disks.
Step-by-Step Configuration Guide for Exchange DAG
Now that we understand what a DAG is, let’s look at the step-by-step configuration process to understand how it can be set up
1. Prepare the Environment
Before you start configuring DAG, you need to ensure that the Exchange Server environment is ready. This includes ensuring that all servers meet the hardware and software requirements, installing the necessary prerequisites, and configuring network settings.
2. Create the DAG
To create a DAG, you need to use the Exchange Management Shell (EMS) or the Exchange Admin Center (EAC). In the EMS, you can use the New-DatabaseAvailabilityGroup cmdlet to create a new DAG or follow the GUI method as described below.
Creating an Exchange DAG – step by step:
- Open the Exchange Management Console (EMC) on one of the Exchange servers.
- In the EMC, navigate to the Organization Configuration node, and select the Mailbox tab.
- Click on the Database Availability Groups tab, and then click New Database Availability Group from the action pane.
- In the New Database Availability Group wizard, enter a name for the DAG, and then click on Next.
- On the Select Servers page, select the servers that you want to include in the DAG.
(Note: The servers must be running the same version of Exchange Server, and the same service pack level)
- On the Configure Database Copies page, you can configure the number of database copies you want to create.
Important: You must create at least one database copy per mailbox database.
- On the Configure Network Settings page, you can configure the DAG’s IP address and subnet mask.
- On the Manage Cluster Core Resources page, select the option to Create a new cluster name and IP address, and then enter the name and IP address for the cluster.
- On the Configure Replication Network page, you can configure the replication network settings.
- Click on New to create the DAG.
- Once the DAG is created, you can add mailbox databases to the DAG by using the Add Mailbox Database Copy wizard.
3. Add Members to the DAG
After creating the DAG, you need to add members to it.
To add a member to the DAG, use the following cmdlet in the EMS or the Add Server Wizard in the EAC.
Or use the following GUI method using EAC.
- Open EAC.
- Go to Servers, then Database Availability Groups.
- Select the DAG that needs to be configured, and then click the option icon.
To add one or more Mailbox servers to the DAG,
- Click on the plus (+) icon.
- Select the required servers from the list
- Click on Add, and then hit OK.
To remove one or more Mailbox servers from the DAG,
- Select the required servers.
- Click the minus (-) icon.
- Click Save to save the changes.
- After the prompt that the task has completed successfully, click Close.
4. Configure the DAG Networks
Once you have added members to the DAG, you need to configure the DAG networks. DAG networks are used to control the flow of replication traffic and ensure that the replication traffic does not interfere with other network traffic.
To configure DAG networks, you can use the following cmdlet in the EMS or the DAG Networks wizard in the EAC.
Alternatively use the following GUI method using EAC
- Open the EAC
- Go to Server, then click on Database Availability Groups.
- Select the DAG networks that need to be configured.
- Under the DAG network that need to be configured in the details pane, choose from the following configuration options.
These options are available only when the Configure database availability group networks is selected from the DAG properties. This step needs to be done manually.
- Disable Replication or Enable Replication
- This option configures the replication settings for the DAG network.
- This option removes a DAG network.
- Prerequisite: Before removing a DAG network, remove all associated subnets from the DAG network, first.
- View details
- This option configures DAG network properties, such as the name, description, and associated subnets for the DAG network. With this, the network interfaces associated with those subnets can also be viewed, and enable or disable replication for the DAG network.
5. Create and Add Mailbox Databases
After configuring the DAG networks, create and add mailbox databases to the DAG.
To create a new mailbox database
- Use the New-MailboxDatabase cmdlet in the EMS or the New Mailbox Database wizard in the EAC.
To add the mailbox database to the DAG
- Use the Add-MailboxDatabaseCopy cmdlet in the EMS or the Add Mailbox Database Copy wizard in the EAC.
6. Test the DAG
Once you have completed the configuration process, it is essential to test the DAG to ensure that it is functioning correctly.
Use the Test-ReplicationHealth cmdlet in the EMS to test the replication health of the DAG.
Monitoring the DAG
After creating a DAG, you need to monitor and manage it regularly to ensure its proper functioning. The following are some of the management tasks that you should perform regularly:
- Monitoring DAG status and replication health
- Testing DAG failover
- Adding or removing mailbox servers from the DAG
- Adding or removing database copies
- Moving database copies between servers
For this purpose, you can use Exchange Reporter Plus. It is a web-based tool used to report on, audit, monitor and perform content search in Exchange Server, Exchange Online and Skype for Business. The DAG monitoring reports include monitoring of replication health , database copy status , DAG network health , activation preference details and more. It features over 450 comprehensive reports on various Exchange objects, such as mailboxes, public folders, and distribution lists. The tool audits granular changes and monitors the server and services 24×7. Alerts in Exchange Reporter Plus give instant notifications on critical events that require your attention.
In conclusion, A Database Availability Group (DAG) is a high availability and disaster recovery solution in Exchange Server. By creating a DAG, you can ensure that your email service remains available even if one or more servers or databases fail. The step-by-step configuration guide outlined in this article will help you create and configure a DAG in your Exchange Server environment.