Hi, 
    I checkout ovirt-engine's code with branch 4.2;  When execute Host's Management --> Active  command,  ovirt engine just set vds's status to "Unassigned" but how the vds's status changed to "UP" in ovirt-engine?  The code in ActiveVdsCommand.executeCommand() as follows:
protected void executeCommand() {

        final VDS vds = getVds();
        try (EngineLock monitoringLock = acquireMonitorLock("Activate host")) {
            executionHandler.updateSpecificActionJobCompleted(vds.getId(), ActionType.MaintenanceVds, false);
            setSucceeded(setVdsStatus(VDSStatus.Unassigned).getSucceeded());

            if (getSucceeded()) {
                TransactionSupport.executeInNewTransaction(() -> {
                    // set network to operational / non-operational
                    List<Network> networks = networkDao.getAllForCluster(vds.getClusterId());
                    networkClusterHelper.setStatus(vds.getClusterId(), networks);
                    return null;
                });

                // Start glusterd service on the node, which would haven been stopped due to maintenance
                if (vds.getClusterSupportsGlusterService()) {
                    runVdsCommand(VDSCommandType.ManageGlusterService,
                            new GlusterServiceVDSParameters(vds.getId(), Arrays.asList("glusterd"), "restart"));
                    // starting vdo service
                    GlusterStatus isRunning = glusterUtil.isVDORunning(vds.getId());
                    switch (isRunning) {
                    case DOWN:
                        log.info("VDO service is down in host : '{}' with id '{}', starting VDO service",
                                vds.getHostName(),
                                vds.getId());
                        startVDOService(vds);
                        break;
                    case UP:
                        log.info("VDO service is up in host : '{}' with id '{}', skipping starting of VDO service",
                                vds.getHostName(),
                                vds.getId());
                           break;
                    case UNKNOWN:
                        log.info("VDO service is not installed host : '{}' with id '{}', ignoring to start VDO service",
                                vds.getHostName(),
                                vds.getId());
                        break;
                    }

                }
            }
        }
    }


Your Sincerely
Mark Lee