NodeJs-stream操作大文件

'use strict'
let fs = require("fs");

fs.readFile("MobyLinuxVM.vhdx", (err, data)=>{
    console.log(err);
});

let reader = fs.createReadStream("MobyLinuxVM.vhdx");
let writer = fs.createWriteStream("MobyLinuxVM-copy.vhdx");
let len = 0;
reader.on('data', (chunk)=>{
    //chunk是每次读取到的一小块字节
    console.log(chunk.length);
    len += chunk.length;
    writer.write(chunk, ()=>{
        console.log("写入了一个chunk");
    })
});
reader.on('end', ()=>{
   console.log("读取完毕,总大小："+len);
});

reader.pipe(writer);