In this blog, I am going to discuss the considerations for configuring a File Share Witness (FSW) for the Failover Cluster hosting your workloads, on a separate Scale-Out File Server cluster. You can find more information on Failover Clustering quorum here.

File Share Witness on a Scale-Out File Server

It is supported to use a file share as a witness that is hosted on a Scale-Out File Server cluster. It is recommended that the following guidelines be considered when configuring your File Share Witness on a Scale-Out File Server:

  • Starting in Windows Server 2012 R2, the recommendation is to always configure a Witness for your cluster. The cluster will now automatically determine if the Witness is to have a vote in determining quorum for the cluster.
  • Create a new Server Message Block (SMB) share on the Scale-Out File Server for the exclusive use of a cluster. Note that the same share can be used for multiple clusters.
  • Ensure that the File Share has a minimum of 5MB provisioned per cluster it is used for.
  • The Scale-Out File Server hosting the file share to be used as a quorum witness should not be created within a Virtual Machine hosted on the same cluster for which the File Share Witness is being created. 
  • Multi-site stretched-clusters:
    • With the Service Level Agreement (SLA) of automatic failover across sites, it is necessary that the Scale-Out File Server backing the File Share Witness be hosted in an independent third site. This enables sites with nodes participating in quorum equal opportunity to survive in case a site experiences a power outage or WAN link connectivity breaks.
    • With the SLA of manual failover across sites, we still recommend that the Scale-Out File Server backing the File Share Witness be hosted in an independent third site. This simplifies the recovery steps necessary in case of a primary site power outage. You may also configure the Scale-Out File Server to be hosted in the primary site. However note that this would require recreating the quorum witness while recovering the cluster from the Backup Disaster Recovery site.
  • Create a non-CA file share for the witness on the Scale-Out File server. A non-CA file share can result in a faster failover of the file share witness resource in the event the Scale-Out File server cluster is unavailable. For a CA share, the file share witness resource may not experience an immediate failure and may only timeout after the 90 second quorum timeout window. On a non-CA share, the file share witness resource will fail immediately, triggering remedial actions from the cluster service. Setting up the configuration for a non-CA share is explained in the next section. 
  • The Scale-Out File Server hosting the File Share Witness should be a member of a domain in the same forest as the cluster it is a Witness for. This is because the Cluster uses the Cluster Name Object to set the permissions on a folder in the share containing the cluster specific information. This ensures that the Cluster has appropriate permissions needed to maintain appropriate cluster state in the share. Additionally, the cluster administrator configuring the File Share Witness needs to have Full Control permissions to the share. This is necessary to set the permissions for the Cluster Name Object to the folder in the share.
  • It is important that the file share created on the Scale-Out File Server is not part of a Distributed File System (DFS) Namespace. The cluster needs to be able to arbitrate a single point for quorum.

 

Configuring a File Share Witness on a Scale-Out File Server

In this section, I will explain how you can create a file share on a Scale-Out File Server that will act as a witness for the cluster hosting your workloads. Therefore, you have two clusters – a “storage” cluster hosting your file share witness and a “compute” cluster hosting your highly available workloads.

You can configure a File Share Witness on a Scale-Out File Server as follows:

1)      Create the Scale-Out File Server as described in Section 2.1 of this article

2)      Create a File share on the Scale-Out File as described in Section 2.2 of this article.

a.       Modify the properties of the share to make it a non-CA share. Right-click on the share, select Settings and uncheck the Enable continuous availability checkbox.

 

b.      Ensure that you have Full Control to the newly created share. 

 

3)     Configure the File Share as a Witness on your cluster

a.       Using the Failover Cluster Manager 

                      
i.     Type cluadmin.msc on an elevated command prompt

                                                     
ii.     Launch the Quorum Wizard by Right-clicking on the Cluster Name, Selecting More Actions and then selecting Configure Quorum Settings                

                                       
iii.     Select Next and then choose the Select the quorum witness option and select Next.   

 

                                                          
iv.     Choose the Configure a file share witness option and select Next.

 

                                                            
v.     Specify the path to the File Share on your Scale-Out File Server and select Next.

 

b.      Using Windows PowerShell

                                                              
i.     Open a Windows PowerShell® console as an Administrator

                    
ii.   Type Set-ClusterQuorum –FileShareWitness <File Share Witness Path>

 

You should now see the File Share Witness configured for your Cluster.

 

When you navigate to your File Share Witness share you will see a folder created for your Cluster.

 

This folder will have permissions for the Cluster Name Object of your “Compute” Cluster so that the entries in the folder can be modified on Cluster membership changes.

 

You will also notice a file Witness.log which contains the membership information for the Cluster.

 

You have now successfully configured a File Share Witness on a Scale-Out File Server, for the cluster hosting your workloads.

 

Thanks!

Subhasish Bhattacharya

Program Manager

Clustering and High Availability

Microsoft