[{"createTime":1735734952000,"id":1,"img":"hwy_ms_500_252.jpeg","link":"https://activity.huaweicloud.com/cps.html?fromacct=261f35b6-af54-4511-a2ca-910fa15905d1&utm_source=V1g3MDY4NTY=&utm_medium=cps&utm_campaign=201905","name":"华为云秒杀","status":9,"txt":"华为云38元秒杀","type":1,"updateTime":1735747411000,"userId":3},{"createTime":1736173885000,"id":2,"img":"txy_480_300.png","link":"https://cloud.tencent.com/act/cps/redirect?redirect=1077&cps_key=edb15096bfff75effaaa8c8bb66138bd&from=console","name":"腾讯云秒杀","status":9,"txt":"腾讯云限量秒杀","type":1,"updateTime":1736173885000,"userId":3},{"createTime":1736177492000,"id":3,"img":"aly_251_140.png","link":"https://www.aliyun.com/minisite/goods?userCode=pwp8kmv3","memo":"","name":"阿里云","status":9,"txt":"阿里云2折起","type":1,"updateTime":1736177492000,"userId":3},{"createTime":1735660800000,"id":4,"img":"vultr_560_300.png","link":"https://www.vultr.com/?ref=9603742-8H","name":"Vultr","status":9,"txt":"Vultr送$100","type":1,"updateTime":1735660800000,"userId":3},{"createTime":1735660800000,"id":5,"img":"jdy_663_320.jpg","link":"https://3.cn/2ay1-e5t","name":"京东云","status":9,"txt":"京东云特惠专区","type":1,"updateTime":1735660800000,"userId":3},{"createTime":1735660800000,"id":6,"img":"new_ads.png","link":"https://www.iodraw.com/ads","name":"发布广告","status":9,"txt":"发布广告","type":1,"updateTime":1735660800000,"userId":3},{"createTime":1735660800000,"id":7,"img":"yun_910_50.png","link":"https://activity.huaweicloud.com/discount_area_v5/index.html?fromacct=261f35b6-af54-4511-a2ca-910fa15905d1&utm_source=aXhpYW95YW5nOA===&utm_medium=cps&utm_campaign=201905","name":"底部","status":9,"txt":"高性能云服务器2折起","type":2,"updateTime":1735660800000,"userId":3}]
HDFS存储机制,包括HDFS的写入过程和读取过程两个部分
读取过程
* 客户端向namenode请求上传文件,namenode检查目标文件是否已经存在,父目录是否存在。
* Namenode向客户端返回是否可以上传。
* 客户端请求第一个block块上传到哪些datanode服务器上。
* Namenode返回三个datanode节点,分别为dn1,dn2,dn3.
* 客户端请求dn1上传数据,dn1收到请求会继续调用dn2,然后dn2调用dn3,将这个通信管道建立完成。
* dn1、dn2、dn3逐级应答客户端。
*
客户端开始往dn1上传第一个block块(先从磁盘读取数据放到一个本地内存缓存),以packet为单位,dn1收到一个packet就会传给dn2,dn2传给dn3;dn1每传一个packet会放入一个应答队列等待应答。
* 每一个block块传输完成之后,客户端在此请求namenode上传第二个block的服务器。((重复执行3-7步)
读数据流程图
写数据
* 客户端向namenode请求下载文件,namenode通过查询元数据,找到文件块所在的datanode地址。
* 挑一台datanode(就近原则,然后随机)服务器,请求读取数据。
* Datanode开始传输数据给客户端(从此盘里读取数据放入流,以packet为单位做校验)。
* 客户端以packet为单位接受,先在本地缓存,然后写入目标文件。
写数据流程图
结语:小编能力有限欢迎大家指正