KB 2144944 Troubleshooting Virtual SAN on-disk format upgrade to 3.0 failures in stretched clusters This video demonstrates how to troubleshoot Virtual SAN on-disk format upgrade to 3.0, which may fail in small Virtual SAN clusters or ROBO/stretched clusters. Attempting an on-disk upgrade in certain VSAN configurations may result in failure. Configurations that can cause these errors are: - The stretched VSAN Cluster consists of two ESXi Hosts and the Witness Node also called ROBO configuration - Each Host in the Stretched Cluster contains a single VSAN Disk Group - A Virtual SAN cluster consists of three normal nodes, with one disk group per node - A Virtual SAN cluster is very full, preventing the full data migration disk-group decommission mode During this upgrade, a single point of failure is exposed. Follow all VMware best practices, and your business practices, regarding the backup of important data and virtual machines. This exposure to additional failure risk is referred to as "reduced redundancy," and must be manually specified in the Ruby vSphere Console or RVC to allow the upgrade to proceed. For additional information, see https://kb.vmware.com/kb/2144944