Install the following packages on the cluster host you choose for NFSv3 Gateway machine (we'll refer to it as the NFS server from here on). The first two items are standard NFS utilities; the last is a CDH package.

• nfs-utils
• nfs-utils-lib
• hadoop-hdfs-nfs3

Proceed as follows, depending on the NFS server's operating system.

$ sudo yum install nfs-utils nfs-utils-lib hadoop-hdfs-nfs3

$ sudo zypper install nfs-utils nfs-utils-lib hadoop-hdfs-nfs3

$ sudo apt-get install nfs-utils nfs-utils-lib hadoop-hdfs-nfs3

Proceed as follows to configure the gateway.

1. Add the following property to hdfs-site.xml on the NameNode:

   <property>
       <name>dfs.namenode.accesstime.precision</name>
       <value>3600000</value>
       <description>The access time for an HDFS file is precise up to this value. The default value is 1 hour.
       Setting a value of 0 disables access times for HDFS.</description>
   </property>
   

2. Add the following property to hdfs-site.xml on the NFS server:

   <property>
     <name>dfs.nfs3.dump.dir</name>
     <value>/tmp/.hdfs-nfs</value>
   </property>

     Note:

   You should change the location of the file dump directory, which temporarily saves out-of-order writes before writing them to HDFS. This directory is needed because the NFS client often reorders writes, and so sequential writes can arrive at the NFS gateway in random order and need to be saved until they can be ordered correctly. After these out-of-order writes have exceeded 1MB in memory for any given file, they are dumped to the dfs.nfs3.dump.dir (the memory threshold is not currently configurable).

   Make sure the directory you choose has enough space. For example, if an application uploads 10 files of 100MB each, dfs.nfs3.dump.dir should have roughly 1GB of free space to allow for a worst-case reordering of writes to every file.

3. Configure the user running the gateway (normally the hdfs user as in this example) to be a proxy for other users. To allow the hdfs user to be a proxy for all other users, add the following entries to core-site.xml on the NameNode:

   <property>
      <name>hadoop.proxyuser.hdfs.groups</name>
      <value>*</value>
      <description>
        Set this to '*' to allow the gateway user to proxy any group.
      </description>
   </property>
   <property>
       <name>hadoop.proxyuser.hdfs.hosts</name>
       <value>*</value>
       <description>
        Set this to '*' to allow requests from any hosts to be proxied.
       </description>
   </property>

4. Restart the NameNode.

To verify that the NFS services are running properly, you can use the rpcinfo command on any host on the local network:

$ rpcinfo -p <nfs_server_ip_address>

You should see output such as the following:

program    vers    proto   port

100005     1       tcp     4242  mountd
100005     2       udp     4242  mountd
100005     2       tcp     4242  mountd
100000     2       tcp     111   portmapper
100000     2       udp     111   portmapper
100005     3       udp     4242  mountd
100005     1       udp     4242  mountd
100003     3       tcp     2049  nfs
100005     3       tcp     4242  mountd

To verify that the HDFS namespace is exported and can be mounted, use the showmount command.

$ showmount -e <nfs_server_ip_address>

You should see output similar to the following:

Exports list on <nfs_server_ip_address>:
/ (everyone)

To import the HDFS file system on an NFS client, use a mount command such as the following on the client:

$ mount -t  nfs  -o vers=3,proto=tcp,nolock <nfs_server_hostname>:/ /hdfs_nfs_mount