code: public VsanUpgradeSystemPreflightCheckResult performVsanUpgradePreflightCheck(ClusterComputeResource cluster, Boolean downgradeFormat) throws RuntimeFault, VsanFault, RemoteException {
          return getVimService().performVsanUpgradePreflightCheck(getMOR(), cluster.getMOR(), downgradeFormat);
      }
docs: Perform an upgrade pre-flight check on a cluster.
  
  @param cluster         The cluster for which to perform the check.
  @param downgradeFormat Intend to perform a on-disk format downgrade instead of upgrade. Adds additional checks.
  @return Pre-flight check result.
  @throws RuntimeFault
  @throws VsanFault
  @throws RemoteException