hdfs是分布式文件系统，要想访问hdfs上的文件，可以用java api或者hadoop shell等工具，如果想操作hdfs文件系统就像操作本地文件系统一样的便捷，可以将hdfs文件系统挂载到本地的一个目录上，可以通过nfs挂载--apache hadoop2.x以后的版本中自带了一个nfs3的插件服务，下面将详细讲解nfs挂载的方式。

官方介绍

http://hadoop.apache.org/docs/r2.5.2/hadoop-project-dist/hadoop-hdfs/HdfsNfsGateway.html

配置core-site.xml

<property>
    <name>hadoop.proxyuser.nfsserver.groups</name>
    <value>*</value>
    <description>允许所有用户组用户代理</description>
</property>
<property>
    <name>hadoop.proxyuser.nfsserver.hosts</name>
    <value>localhost</value>
    <description>允许挂载的主机域名</description>
</property>
</property>

修改hdfs-site.xml

<property>
    <name>nfs.dump.dir</name>
    <value>/tmp/.hdfs-nfs</value>
</property>
<property>
    <name>nfs.rtmax</name>
    <value>1048576</value>
    <description>This is the maximum size in bytes of a READ request supported by the NFS gateway. If you change this, make sure you also update the nfs mount's rsize(add rsize= # of bytes to the mount directive).</description>
</property>
<property>
    <name>nfs.wtmax</name>
    <value>65536</value>
    <description>This is the maximum size in bytes of a WRITE request supported by the NFS gateway. If you change this, make sure you also update the nfs mount's wsize(add wsize= # of bytes to the mount directive).</description>
</property>
<property>
    <name>nfs.exports.allowed.hosts</name>
    <value>* rw</value>
    <description>允许所有主机对文件有rw权限</description>
</property>

重启hadoop集群服务

关闭本机的nfs以及rpcbind服务

启动hadoop portmap和nfs3,需要root权限

[root@master ~]# /home/hadoop/hadoop-2.7.3/sbin/hadoop-daemon.sh start portmap
[root@master ~]# /home/hadoop/hadoop-2.7.3/sbin/hadoop-daemon.sh start nfs3

查看本机挂载状况

[root@master ~]# showmount -e localhost
Export list for localhost:
/ *

可以在其他未安装HDFS的机器上通过nfs挂载hdfs目录

# mount -t nfs -o vers=3,proto=tcp 10.10.18.229:/ /mnt
# ls /mnt/user
hadoop  hive  spark

测试速度
大概每秒40M，感觉不理想

[root@localhost brute_force]# time cp /mnt/shegong.txt .

real    6m23.823s
user    0m0.014s
sys 0m23.255s
[root@localhost brute_force]# du -msh /mnt/shegong.txt 
15G /mnt/shegong.txt
[root@localhost brute_force]# du -msh /mnt/shegong.txt ./shegong.txt 
15G /mnt/shegong.txt
15G ./shegong.txt