What is the urgency of adding quorum/witness on Always On High Availability?

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What is the urgency of adding quorum/witness on Always On High Availability?

Fadjar Syamali 21

based on this article,

In an HA configuration, a cluster role is created for every availability group that you create. The WSFC cluster monitors this role to evaluate the health of the primary replica. The quorum for Always On availability groups is based on all nodes in the WSFC cluster regardless of whether a given cluster node hosts any availability replicas. In contrast to database mirroring, there is no witness role in Always On availability groups.

https://learn.microsoft.com/en-us/sql/database-engine/availability-groups/windows/overview-of-always-on-availability-groups-sql-server?view=sql-server-ver15

is there any objective or urgency to add quorum/witness on Always On High Availability Groups?

What the purposes of adding new server dedicated for quorum/witness on Always On High Availability Groups?

YufeiShao-msft 7,146 Reputation points

2021-12-06T01:03:08.167+00:00

Could you please validate all the answers so far and provide any update?
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YufeiShao-msft 7,146 Reputation points

2021-12-06T01:03:08.167+00:00

Could you please validate all the answers so far and provide any update?
Please remember to accept the answers if they helped. Your action would be helpful to other users who encounter the same issue and read this thread.

Thank you for understanding!

Answer 1

YufeiShao-msft 7,146

Hi @Fadjar Syamali

is there any objective or urgency to add quorum/witness on Always On High Availability Groups?

you can read this article
Quorum is a mechanism that helps ensure that WSFC is up and running through ensuring enough resources are online in the WSFC. If the WSFC has enough votes, it is healthy and able to provide 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 presence of a quorum means that the cluster is healthy and able to provide node-level fault tolerance.

Whenever a witness is set for a database mirroring session, quorum is required, as long as the current principal server has quorum, this server owns the role of principal and continue to serve the database, if the principal server loses quorum, it stops serving the database

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Fadjar Syamali 21 Reputation points

2021-11-30T03:03:53.647+00:00

Thank you for the answers!

In my case, i have 2 node in DC (sync commit), and 2 node in DRC(async commit)

is there still need to have additional quorum/witness server on my AG environment?
YufeiShao-msft 7,146 Reputation points

2021-11-30T06:02:26.843+00:00

Hi, you can refer to this article, if you have three or four nodes, witness is strongly recommended. the concept of majority only works cleanly when the total number of nodes in the cluster is odd
Fadjar Syamali 21 Reputation points

2021-11-30T07:04:12.157+00:00

Thank you @YufeiShao-msft for the explanation and reference, it clearly answer my question!
YufeiShao-msft 7,146 Reputation points

2021-11-30T07:11:36.06+00:00

Hi @Fadjar Syamali ，
Please do not forget to mark as accepted answer wherever information provided to you were helpful.

Thank you for understanding!

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What is the urgency of adding quorum/witness on Always On High Availability?

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