Unable to remove host from cluster with precheck error indicating “due to vSAN requirements”

Products

• VMware vSAN

Issue/Introduction

While attempting precheck for placing host into Maintenance Mode with the vSAN full evacuation option, the vCenter UI vSAN maintenance mode precheck displayed the message that the "host cannot enter Maintenance Mode due to vSAN requirements".

Environment

vSAN 7.x
vSAN 8.x

Cause

There is not enough hosts/fault domains to meet minimum requirements for vSAN storage policy on all of the objects in the cluster. The chart below displays the minimum requirements for various storage policies. 

Resolution

Change the storage policy on objects where the assigned policy requires more hosts than will be available once a host is in Maintenance Mode. 

Example: Change Raid 6 object to Raid 5 or Raid 1 Failures to Tolerate 2 object to Raid 1 Failures to Tolerate 1.

Additional Information

You may verify all of the VMs are using a compatible policy in the Policies and Profiles section of vCenter.
If further assistance is needed in identifying what objects may be preventing entering maintenance mode 

See the following tech docs pages for more details:
Managing Fault Domains in vSAN Clusters
What are vSAN Policies