code: public void allocate(long size) throws IOException, ServerException {
          Command cmd = new Command("ALLO", String.valueOf(size));
          Reply reply = null;
          try {
              reply = controlChannel.execute(cmd);
          } catch (UnexpectedReplyCodeException urce) {
              throw ServerException.embedUnexpectedReplyCodeException(urce);
          } catch (FTPReplyParseException rpe) {
              throw ServerException.embedFTPReplyParseException(rpe);
          }
      }
docs: Reserve sufficient storage to accommodate the new file to be
  transferred.
  
  @param     size the amount of space to reserve
  @exception ServerException if an error occured.