Ozone File System

There are many Hadoop compatible files systems under Hadoop. Hadoop compatible file systems ensures that storage backends like Ozone can easily be integrated into Hadoop eco-system.

Setting up the Ozone file system

To create an ozone file system, we have to choose a bucket where the file system would live. This bucket will be used as the backend store for OzoneFileSystem. All the files and directories will be stored as keys in this bucket.

Please run the following commands to create a volume and bucket, if you don’t have them already.

ozone sh volume create /volume
ozone sh bucket create /volume/bucket

Once this is created, please make sure that bucket exists via the listVolume or listBucket commands.

Please add the following entry to the core-site.xml.

<property>
  <name>fs.o3fs.impl</name>
  <value>org.apache.hadoop.fs.ozone.OzoneFileSystem</value>
</property>
<property>
  <name>fs.defaultFS</name>
  <value>o3fs://bucket.volume</value>
</property>

This will make this bucket to be the default file system for HDFS dfs commands and register the o3fs file system type.

You also need to add the ozone-filesystem.jar file to the classpath:

export HADOOP_CLASSPATH=/opt/ozone/share/ozonefs/lib/hadoop-ozone-filesystem-lib-current*.jar:$HADOOP_CLASSPATH

Once the default Filesystem has been setup, users can run commands like ls, put, mkdir, etc. For example,

hdfs dfs -ls /

or

hdfs dfs -mkdir /users

Or put command etc. In other words, all programs like Hive, Spark, and Distcp will work against this file system. Please note that any keys created/deleted in the bucket using methods apart from OzoneFileSystem will show up as directories and files in the Ozone File System.

Note: Bucket and volume names are not allowed to have a period in them. Moreover, the filesystem URI can take a fully qualified form with the OM host and port as a part of the path following the volume name. For example,

hdfs dfs -ls o3fs://bucket.volume.om-host.example.com:5678/key

Supporting older Hadoop version (Legacy jar, BasicOzoneFilesystem)

There are two ozonefs files, both of them include all the dependencies:

  • share/ozone/lib/hadoop-ozone-filesystem-lib-current-VERSION.jar
  • share/ozone/lib/hadoop-ozone-filesystem-lib-legacy-VERSION.jar

The first one contains all the required dependency to use ozonefs with a compatible hadoop version (hadoop 3.2).

The second one contains all the dependency in an internal, separated directory, and a special class loader is used to load all the classes from the location.

With this method the hadoop-ozone-filesystem-lib-legacy.jar can be used from any older hadoop version (eg. hadoop 3.1, hadoop 2.7 or spark+hadoop 2.7)

Similar to the dependency jar, there are two OzoneFileSystem implementation.

For hadoop 3.0 and newer, you can use org.apache.hadoop.fs.ozone.OzoneFileSystem which is a full implementation of the Hadoop compatible File System API.

For Hadoop 2.x you should use the Basic version: org.apache.hadoop.fs.ozone.BasicOzoneFileSystem.

This is the same implementation but doesn’t include the features/dependencies which are added with Hadoop 3.0. (eg. FS statistics, encryption zones).

Summary

The following table summarize which jar files and implementation should be used:

Hadoop version Required jar OzoneFileSystem implementation
3.2 filesystem-lib-current org.apache.hadoop.fs.ozone.OzoneFileSystem
3.1 filesystem-lib-legacy org.apache.hadoop.fs.ozone.OzoneFileSystem
2.9 filesystem-lib-legacy org.apache.hadoop.fs.ozone.BasicOzoneFileSystem
2.7 filesystem-lib-legacy org.apache.hadoop.fs.ozone.BasicOzoneFileSystem

With this method the hadoop-ozone-filesystem-lib-legacy.jar can be used from any older hadoop version (eg. hadoop 2.7 or spark+hadoop 2.7)