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DAG Failover Not Working with 2-Node Exchange Servers 2019 cu15 on server 2025

parisa moghadam 5 Reputation points
2025-04-14T09:39:13.1233333+00:00

Hi,

I have a Database Availability Group (DAG) configured with two Exchange servers: EMAIL01 and EMAIL02. Everything appears to be set up correctly — both servers are members of the DAG, and the witness server is configured.

However, when I shut down one of the servers (for example, EMAIL01), the other server (EMAIL02) does not take over. The databases do not mount automatically, and Exchange services are disrupted.

I've checked the DAG membership, cluster status, and witness availability, and all seem okay. I'm unsure why failover doesn't occur as expected.

Any suggestions on what might be wrong or what else I should check?

Thanks!

Exchange | Exchange Server | Management

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  1. Amit Singh 5,306 Reputation points
    2025-04-16T05:02:17.9133333+00:00

    Hi @parisa moghadam,

    This is a common snag with 2-node DAGs, and you're right to focus on the witness server and cluster status — but there are a couple key things to double-check:

    – In a 2-node DAG, the witness server becomes critical for maintaining quorum. If the active server goes down and the remaining one can't reach the witness, it won't have quorum, and databases won’t mount. Make sure:

    The witness server is online and reachable from EMAIL02.

    The Exchange Trusted Subsystem group has local admin rights on the witness.

    – Verify the quorum configuration is set to Node and File Share Majority. You can confirm this with:

    Get-Cluster | fl Name,Quorum*

    If quorum is misconfigured, failover won’t happen.

    – Check if EMAIL02 is marked as a lower activation preference or if there's a lag setting preventing immediate mount:

    Get-MailboxDatabaseCopyStatus *

    – Make sure automatic activation isn’t blocked on EMAIL02:

    Get-MailboxServer EMAIL02 | fl DatabaseCopyAutoActivationPolicy

    It should be Unrestricted.

    Let us know what you find — it usually comes down to quorum loss or an activation block.

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