Exchange 2010 DAG Members and Cluster Quorum Configuration

Many a times I was asked If the cluster Quorum is configured properly. Their has been questions around Quorum configuration and number of  nodes in DAG ( Database Availability Group) , number of nodes in Cluster and the cluster quorum configuration type.  This Blog post discuss more on Cluster configuration.

Exchange 2010 decides on one of these quorum models, depending on number of nodes in DAG. 

IMPORTANT: In most situations, use the quorum configuration that the cluster identifies as appropriate for your cluster. Change the quorum configuration only if you have determined that the change is appropriate for your cluster. You can easily let cluster determine the type of quorum to be used by running exchange cmdlet Set-Databaseavailabilitygroup …… with appropriate parameters.

Following example shows how cluster quorum is automatically determined based on number of nodes.On Adding 5 nodes to the creates the FSW on adding  2 and 4 node , switch to Node majority on adding  1,3,5 node to the cluster.

A- Create a DAG Object and Add first Node to Cluster

Add-databaseavailabilitygroupserver “Contoso-DAG” –Mailboxserver  Server1                                                                                                   

2 – Adding  Second Mailbox Server to the DAG and Node 2 to cluster

Add-databaseavailabilitygroupserver “Contoso-DAG” –mailboxserver Server2

Adding second node to DAG from Exchange management shell or GUI configures the FSW Automatically , because now we have even nodes 

3 – Adding Mailbox Server 3 to the DAG and node 3 to cluster

Add-databaseavailabilitygroupserver “Contoso-DAG” –mailboxserver Server3

D – Adding fourth Mailbox Server to the DAG [ * Even number of nodes ] / Node 4 to the cluster configures FSW resource automatically

Add-databaseavailabilitygroupserver “Contoso-DAG” –mailboxserver Server4

FSW resource is added back to the cluster automatically

E – Adding Fifth node to the DAG . , quorum will be set to Node Majority , based on number of nodes in cluster .[ *Odd number ]

This is how cluster and DAG looks at the end of adding 5 nodes .

   * sometimes you may change the Quorum configuration manual. to fix your quorum model , run following cmdlet . Exchange  internally calls use the cluster API, which validate quorum model based on number of nodes in Cluster.

Set-databaseavailabilitygroup yourdagname –witnessserver “servername”  -witnessdirectory “c:\witness”

  This functionality is documented here, : https://technet.microsoft.com/en-us/library/cc770620(WS.10).aspx

- Manju

Comments

• Anonymous
  October 24, 2013
  Thanks Manju. This is what I was look for long time. so you mean to say in a three node DAG the cluster will survive if two nodes are getting failed.

• Anonymous
  October 24, 2013
  Nope, when majority is lost cluster will fail and the DAG. when you have a single node in DAG without majority, you need to perform a recovery to the single node. first step is to recover cluster service using /forcequorum or restore-dag.. switch depending on your configuration and rest of the steps should follow accordingly depending on your configuration. ( DAC or Non-DAC) if majority is lost while forming quorum, cluster will fail. additionally you can check for dynamic quorum concept in W2012, should help

• Anonymous
  January 22, 2015
  Hi Manju
  
  I have a little doubt
  
  I Have a 3 nodes in a dag.quorum configured as majority node
  
  If I simulate a fault, switch off n1and n2, node 3 remain online.
  I see on node3 all dtabase dismounted and quorum lost. My hub transport are online.
  In this case it's necessary to manually change quorum configuration?
  
  Cheers
  Maximilian

• Anonymous
  March 17, 2015
  Hi Maxmilian,
  
  If the DAG has a single node up should be a minority and the cluster service itself fails.
  In this case you have to force start the DAG to run on a single node but it is not recommended.
  You can add an another mailbox server in DAG which is configured as Dummy with no databases are configured.
  This is only for voting purpose so the DAG will not fails.
  
  Cheers
  Shafi.H

• Anonymous
  July 13, 2015
  Hi Manju,
  
  If you're running the 5 node DAG (cluster) and it's in Node Majority Quorum model is it at all dynamic when a node goes offline; will it fall back to the Witness for the extra vote? I doubt it but thought I'd ask. I can foresee a scenario where in a 4 node DAG stretched across 2 datacenters & using a witness a sever has to go offline for a lengthy period. You might quickly add another dummy MB server to the DAG trying to maintain quorum in case of a WAN outage, but this will then exclude the witness from counting as a vote.
  
  Let me know what you think. Thanks.
  
  Steven

• Anonymous
  October 26, 2015
  i got a 3 node dag 2 in Primary and 1 as a failover on another datacenter, No DAC mode. yet when i restart or shutdown 1 node, no matter if its on the primary site or DR site, The Quorum is lost and the DB's are dismounted. Anyone seen this behavior before?

• Anonymous
  October 26, 2015
  Curibe,
  This one looks like issues with your network configuration. when one of the node is down, check event logs and clusters to see what else is going on that is bringing down the entire cluster.