@Override
public NamenodeCommand startCheckpoint(NamenodeRegistration registration)
throws IOException {
StartCheckpointRequestProto req = StartCheckpointRequestProto.newBuilder()
.setRegistration(PBHelper.convert(registration)).build();
NamenodeCommandProto cmd;
try {
cmd = rpcProxy.startCheckpoint(NULL_CONTROLLER, req).getCommand();
} catch (ServiceException e) {
throw ProtobufHelper.getRemoteException(e);
}