Below is a step-by-step guide on how to add a third node to an existing 2-node Storage Spaces Direct (S2D) cluster with the production workload still running.

1.) Ensure that the cluster is configured with a witness.

2.) Pause/Drain a node in the cluster.

3.) Place the paused node's drives into a storage maintenance mode.

Get-StorageFaultDomain -type StorageScaleUnit | Where-Object {$_.FriendlyName -eq “<Node Name>”} | Enable-StorageMaintenanceMode 

4.) Physically add the 3rd node into the 2-node cluster configuration by cabling the three servers like the image below:

DataON 2U Platforms:

DataON 1U Platform:

5.) Make sure the node that is being added to the cluster has the same firmware and drivers installed as the two servers in the existing 2-node cluster. Also install the necessary Windows features and configure the network correctly. Before adding the third node to the cluster, run a cluster validation.

$S1 = "Node1"

$S2 = "Node2"

$S3 = "Node3"

$nodes = ($S1,$S2,$S3)

Test-Cluster -node $nodes -Include "Storage Spaces Direct",Inventory,Network, "System Configuration" -ReportName C:\Windows\cluster\Reports\report

6.) With a clean validation report, proceed to add the third node into the S2D cluster.

<<Add-ClusterNode -Name ‘NewNodeName’ >>

7.) Disable the storage maintenance mode on the drives of the paused node; Resume the node to the cluster.

Get-StorageFaultDomain -type StorageScaleUnit | Where-Object {$_.FriendlyName -eq “<Node Name>”} | Disable-StorageMaintenanceMode 

8.) By adding a third node to the S2D cluster, 3-way-mirror resiliency is unlocked; Run the following command to configure this setting on the existing storage pool.

<< Get-StoragePool S2D* | Get-ResiliencySetting -Name Mirror | Set-ResiliencySetting -PhysicalDiskRedundancyDefault 2>>

9.) Allow S2D optimization job to complete as well as any other storage jobs to finish before creating a new 3-way-mirror virtual disk/CSV.

10.) With the increased capacity from joining the third node to the cluster, you may now create a new volume (3-way-mirror).

NOTE: The virtual disks that were previously created will remain as 2-way-mirror resiliency.