Adding 4th node AO fails

Question

Hi guys,

I have the following config;

2 W2012R2std\SQL2016ent servers and I want to migrate to 2 W2016dc\SQL2019ent and after that completed to W2019dc\SQL2019ent
Windows cluster level is W2012R2 and finally level W2019
within SSMS I add a 3rd replica, all goes well
when adding the 4th replica, message this is the 4th node and a max of 3 is allowed, unfortunately no screenshot :-(
but it is SQLent edition, so max of 8 is allowed

I really don't understand why this is happening.
Especaillay because I did it before but then with SQLdev as the main difference.

I hope somebody can clarify this issue for me.

kind regards
Marco

Answer 1

Hi @Marco Bakker,

Can you ping between nodes? Make sure that the fourth replica can communicate with the other three replicas and that all necessary ports are open.

Did you join the Windows cluster for this node? You can check the specifics via Failover Configuration Manager. The cluster log in there will record some error messages.

In the case of four nodes, you also need to configure the Quorum mechanism.

Windows Server Failover Clustering (WSFC) uses a quorum-based approach to monitoring overall cluster health and maximize node-level fault tolerance. A quorum node set is a majority of the voting nodes and witnesses in the WSFC cluster. The overall health and status of a WSFC cluster is determined by a periodic quorum vote. The four nodes will appear 2-to-2.

Please refer to this article:

https://www.sqlshack.com/windows-failover-cluster-quorum-modes-in-sql-server-always-on-availability-groups/

In addition, here is a MS document:

https://learn.microsoft.com/en-us/sql/sql-server/failover-clusters/windows/wsfc-quorum-modes-and-voting-configuration-sql-server?view=sql-server-ver16

Best regards,

Seeya

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