Configuring Witness Server in Exchange Server

Witness Server, is a component used to provide DAG (high availability) in the Microsoft Exchange Server infrastructure. In particular, Database Availability Group (DAG) It comes into play in cases where the majority decision cannot be taken in their structures.

In scenarios where the number of member servers in the DAG is even, the Witness Server determines the majority by providing an extra voting right and supports the uninterrupted operation of the system.

What is Witness Server?

Witness Server is a server that will help you make a majority decision among DAG members. In cases where the number of member servers in the DAG is even, and the majority is not reached, the Witness Server will help you make a decision by voting.

Note: Only relevant DAG members have access to the Witness folder.

Function of Witness Server

Exchange Server'of DAY structure is a mechanism for ensuring business continuity by backing up the databases of multiple servers. DAY Its members determine the active site by providing the majority in the system. However, in cases where the number of members is even, the decision-making mechanism may be disrupted.. Here it is Witness Server comes into play and plays a critical role in keeping the system running.

It is vital that the Witness Server is placed in the correct location. If the Witness Server is located in the same physical location as the primary data center, it may be disabled during a potential site outage. Therefore:

Exchange Server Witness Server Scenario

Below is an example scenario that explains how Witness Server works across two different data centers and how it contributes to business continuity.

Scenario Description:

  • Datacenter 1 (Istanbul): Active site with 5 Exchange Servers.
  • Datacenter 2 (Ankara): Passive site with 5 Exchange Servers.
  • Total DAG Structure: 10 servers.
  • Majority Requirement: In a 10-server structure, 6 active votes are required to achieve a majority.

Event:

A sudden power outage occurs in the data center in Istanbul, completely shutting down 5 servers there. The servers in Ankara are still operational, but 5 servers are not enough to provide a majority.

Steps for Witness Server to come into play:

  1. Servers in Ankara refer to Witness Server.
    • The Witness Server attempts to communicate with the servers in Istanbul but fails.
  2. Witness Server gives an extra vote to servers in Ankara.
    • Thanks to this extra vote, servers in Ankara reach 6 votes.
  3. The majority is achieved and the servers in Ankara become active.
    • The system continues to operate without interruption.

Note: If the Witness Server was also located in Istanbul, it would be affected by the power outage. Therefore, it is recommended to have the Witness Server in a different location, preferably at equal distance from both data centers.

Configuring Witness Server in Exchange Server

You can follow the steps below to configure Witness Server: To create a Witness Server on an Exchange Server, you will need to make the relevant server a member of the Exchange Trusted Subsystem.

  1. computer Management open the interface.
    • Select the server to be used as the Witness Server.
  2. Exchange Trusted Subsystem Add the group to local administrators (Local Admin).
    • This will give DAG members access to the Witness Server folder.
  3. Define Witness Server during DAG Configuration.
    • The defined folders and shares must be accessible only to DAG members.
Exchange Trusted Subsystem
Microsoft recommends that you do not use your Domain Controller servers as File Share Witness Servers. 

We will continue with the next process of creating a DAG in Exchange Server. When a Witness Server is configured and positioned correctly in Exchange Server, it ensures uninterrupted system operation in emergency situations such as data center outages.

Resolving DAG Witness Failed State error in Exchange Server environment You can click on the link for.


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