Two node vSAN cluster, failed maintenance mode precheck with: Not enough fault domains.

Products

• VMware vSAN

Issue/Introduction

When attempting to enter maintenance mode using ensure accessibility on a two node vSAN cluster. 

• Fails with 'General vSAN error while entering maintenance mode' and maintenance mode pre-check states 'Not enough Fault Domains' 

Environment

vSAN 6.x

vSAN 7.x

vSAN 8.x

Cause

vSAN storage policy option for Site Disaster Tolerance : "Keep data on preferred site" or "Keep data on secondary site" is set for one or more VMs on a 2-node cluster. 

Resolution

Confirm the vSAN policies for all the VMs are compliant and have 'Site Disaster Tolerance' option selected as 'Raid 1 (Mirroring)'. 

 

*For two node vSAN clusters, avoid the site disaster tolerance options "Keep data on Preferred (stretched cluster)" and "Keep data on Secondary (stretched cluster)". Attempting to place a host into maintenance mode where it has one of these in use, may cause it to fail. This is because objects set with this policy can only run on a host in secondary or primary domain (depending on the policy). 

This tolerance option is more intended for multiple hosts are available in the primary/secondary domains for a fully established stretch cluster of at least four or more hosts. Using this in a 2-node will result vSAN unable to enter maintenance mode, as there is only one host in Primary and one host in Secondary. 

Additional Information

Using vSAN policies (Documentation).

• Site disaster tolerance: None - keep data on Preferred (stretched cluster). If you do not want the objects in a vSAN stretched cluster to have site failure tolerance and you want to make the objects accessible only on the site that is configured as Preferred, use this option.
• Site disaster tolerance: None - keep data on Secondary (stretched cluster). If you do not want the objects in a vSAN stretched cluster to have site failure tolerance and you want to make the objects accessible only on the secondary site, use this option. These objects are not affected by the Inter-Switch Link (ISL) or witness host failures. They remain accessible if the site chosen by the policy is accessible.
  
  

*Do not use these on a two node vSAN cluster.