text: var fs = require('fs');
  var ws = fs.createWriteStream('./test.txt',{
      highWaterMark:16
  });// 16k
  writeMillion(ws,'data','utf8',function(){});
  function writeMillion(writer,data,encoding,callback){
    var i = 1000000;
    write();
    function write(){
      var ok = true;
        do{
            i -= 1;
            if(i == 0){
                writer.write(data,encoding,callback);
            }else{
                ok = writer.write(data,encoding);
                console.log(ok);
            }
        }while(i>0 && ok)
        if(i>0){
            writer.once('drain',write);
        }
    }
  }
  