HDFS-5347. Add HDFS NFS user guide. Contributed by Brandon Li
git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1534377 13f79535-47bb-0310-9956-ffa450edef68
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Brandon Li
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@ -422,6 +422,8 @@ Release 2.2.1 - UNRELEASED
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and range in error message. (Kousuke Saruta via suresh)
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HDFS-5365. Fix libhdfs compile error on FreeBSD9. (Radim Kolar via cnauroth)
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HDFS-5347. Add HDFS NFS user guide. (brandonli)
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Release 2.2.0 - 2013-10-13
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@ -0,0 +1,258 @@
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~~ Licensed under the Apache License, Version 2.0 (the "License");
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~~ you may not use this file except in compliance with the License.
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~~ You may obtain a copy of the License at
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~~
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~~ http://www.apache.org/licenses/LICENSE-2.0
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~~
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~~ Unless required by applicable law or agreed to in writing, software
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~~ distributed under the License is distributed on an "AS IS" BASIS,
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~~ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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~~ See the License for the specific language governing permissions and
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~~ limitations under the License. See accompanying LICENSE file.
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---
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Hadoop Distributed File System-${project.version} - HDFS NFS Gateway
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---
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---
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${maven.build.timestamp}
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HDFS NFS Gateway
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\[ {{{./index.html}Go Back}} \]
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%{toc|section=1|fromDepth=0}
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* {Overview}
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The NFS Gateway supports NFSv3 and allows HDFS to be mounted as part of the client's local file system.
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Currently NFS Gateway supports and enables the following usage patterns:
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* Users can browse the HDFS file system through their local file system
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on NFSv3 client compatible operating systems.
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* Users can download files from the the HDFS file system on to their
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local file system.
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* Users can upload files from their local file system directly to the
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HDFS file system.
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* Users can stream data directly to HDFS through the mount point. File
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append is supported but random write is not supported.
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The NFS gateway machine needs the same thing to run an HDFS client like Hadoop JAR files, HADOOP_CONF directory.
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The NFS gateway can be on the same host as DataNode, NameNode, or any HDFS client.
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* {Configuration}
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NFS gateway can work with its default settings in most cases. However, it's
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strongly recommended for the users to update a few configuration properties based on their use
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cases. All the related configuration properties can be added or updated in hdfs-site.xml.
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* If the client mounts the export with access time update allowed, make sure the following
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property is not disabled in the configuration file. Only NameNode needs to restart after
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this property is changed. On some Unix systems, the user can disable access time update
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by mounting the export with "noatime".
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----
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<property>
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<name>dfs.access.time.precision</name>
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<value>3600000</value>
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<description>The access time for HDFS file is precise upto this value.
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The default value is 1 hour. Setting a value of 0 disables
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access times for HDFS.
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</description>
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</property>
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----
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* Users are expected to update the file dump directory. NFS client often
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reorders writes. Sequential writes can arrive at the NFS gateway at random
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order. This directory is used to temporarily save out-of-order writes
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before writing to HDFS. For each file, the out-of-order writes are dumped after
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they are accumulated to exceed certain threshold (e.g., 1MB) in memory.
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One needs to make sure the directory has enough
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space. For example, if the application uploads 10 files with each having
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100MB, it is recommended for this directory to have roughly 1GB space in case if a
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worst-case write reorder happens to every file. Only NFS gateway needs to restart after
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this property is updated.
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----
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<property>
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<name>dfs.nfs3.dump.dir</name>
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<value>/tmp/.hdfs-nfs</value>
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</property>
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----
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* By default, the export can be mounted by any client. To better control the access,
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users can update the following property. The value string contains machine name and
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access privilege, separated by whitespace
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characters. Machine name format can be single host, wildcards, and IPv4 networks.The
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access privilege uses rw or ro to specify readwrite or readonly access of the machines to exports. If the access
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privilege is not provided, the default is read-only. Entries are separated by ";".
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For example: "192.168.0.0/22 rw ; host*.example.com ; host1.test.org ro;". Only NFS gateway needs to restart after
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this property is updated.
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----
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<property>
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<name>dfs.nfs.exports.allowed.hosts</name>
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<value>* rw</value>
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</property>
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----
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* Customize log settings. To get NFS debug trace, users can edit the log4j.property file
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to add the following. Note, debug trace, especially for ONCRPC, can be very verbose.
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To change logging level:
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-----------------------------------------------
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log4j.logger.org.apache.hadoop.hdfs.nfs=DEBUG
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-----------------------------------------------
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To get more details of ONCRPC requests:
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-----------------------------------------------
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log4j.logger.org.apache.hadoop.oncrpc=DEBUG
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-----------------------------------------------
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* {Start and stop NFS gateway service}
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Three daemons are required to provide NFS service: rpcbind (or portmap), mountd and nfsd.
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The NFS gateway process has both nfsd and mountd. It shares the HDFS root "/" as the
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only export. It is recommended to use the portmap included in NFS gateway package. Even
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though NFS gateway works with portmap/rpcbind provide by most Linux distributions, the
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package included portmap is needed on some Linux systems such as REHL6.2 due to an
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{{{https://bugzilla.redhat.com/show_bug.cgi?id=731542}rpcbind bug}}. More detailed discussions can
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be found in {{{https://issues.apache.org/jira/browse/HDFS-4763}HDFS-4763}}.
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[[1]] Stop nfs/rpcbind/portmap services provided by the platform (commands can be different on various Unix platforms):
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-------------------------
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service nfs stop
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service rpcbind stop
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-------------------------
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[[2]] Start package included portmap (needs root privileges):
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-------------------------
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hadoop portmap
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OR
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hadoop-daemon.sh start portmap
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-------------------------
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[[3]] Start mountd and nfsd.
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No root privileges are required for this command. However, ensure that the user starting
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the Hadoop cluster and the user starting the NFS gateway are same.
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-------------------------
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hadoop nfs3
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OR
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hadoop-daemon.sh start nfs3
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-------------------------
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Note, if the hadoop-daemon.sh script starts the NFS gateway, its log can be found in the hadoop log folder.
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[[4]] Stop NFS gateway services.
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-------------------------
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hadoop-daemon.sh stop nfs3
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hadoop-daemon.sh stop portmap
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-------------------------
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* {Verify validity of NFS related services}
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[[1]] Execute the following command to verify if all the services are up and running:
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-------------------------
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rpcinfo -p $nfs_server_ip
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-------------------------
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You should see output similar to the following:
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-------------------------
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program vers proto port
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100005 1 tcp 4242 mountd
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100005 2 udp 4242 mountd
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100005 2 tcp 4242 mountd
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100000 2 tcp 111 portmapper
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100000 2 udp 111 portmapper
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100005 3 udp 4242 mountd
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100005 1 udp 4242 mountd
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100003 3 tcp 2049 nfs
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100005 3 tcp 4242 mountd
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-------------------------
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[[2]] Verify if the HDFS namespace is exported and can be mounted.
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-------------------------
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showmount -e $nfs_server_ip
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-------------------------
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You should see output similar to the following:
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-------------------------
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Exports list on $nfs_server_ip :
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/ (everyone)
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-------------------------
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* {Mount the export “/”}
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Currently NFS v3 only uses TCP as the transportation protocol.
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NLM is not supported so mount option "nolock" is needed. It's recommended to use
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hard mount. This is because, even after the client sends all data to
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NFS gateway, it may take NFS gateway some extra time to transfer data to HDFS
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when writes were reorderd by NFS client Kernel.
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If soft mount has to be used, the user should give it a relatively
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long timeout (at least no less than the default timeout on the host) .
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The users can mount the HDFS namespace as shown below:
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-------------------------------------------------------------------
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mount -t nfs -o vers=3,proto=tcp,nolock $server:/ $mount_point
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-------------------------------------------------------------------
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Then the users can access HDFS as part of the local file system except that,
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hard link and random write are not supported yet.
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* {User authentication and mapping}
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NFS gateway in this release uses AUTH_UNIX style authentication. When the user on NFS client
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accesses the mount point, NFS client passes the UID to NFS gateway.
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NFS gateway does a lookup to find user name from the UID, and then passes the
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username to the HDFS along with the HDFS requests.
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For example, if the NFS client has current user as "admin", when the user accesses
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the mounted directory, NFS gateway will access HDFS as user "admin". To access HDFS
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as the user "hdfs", one needs to switch the current user to "hdfs" on the client system
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when accessing the mounted directory.
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The system administrator must ensure that the user on NFS client host has the same
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name and UID as that on the NFS gateway host. This is usually not a problem if
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the same user management system (e.g., LDAP/NIS) is used to create and deploy users on
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HDFS nodes and NFS client node. In case the user account is created manually in different hosts, one might need to
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modify UID (e.g., do "usermod -u 123 myusername") on either NFS client or NFS gateway host
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in order to make it the same on both sides. More technical details of RPC AUTH_UNIX can be found
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in {{{http://tools.ietf.org/html/rfc1057}RPC specification}}.
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@ -80,6 +80,7 @@
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<item name="HttpFS Gateway" href="hadoop-hdfs-httpfs/index.html"/>
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<item name="Short Circuit Local Reads"
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href="hadoop-project-dist/hadoop-hdfs/ShortCircuitLocalReads.html"/>
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<item name="HDFS NFS Gateway" href="hadoop-project-dist/hadoop-hdfs/HdfsNfsGateway.html"/>
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</menu>
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<menu name="MapReduce" inherit="top">
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