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Ozone - Object store for Hadoop
Introduction
Ozone is an object store for Hadoop. It is a redundant, distributed object store build by leveraging primitives present in HDFS. Ozone supports REST API for accessing the store.
Getting Started
Ozone is a work in progress and currently lives in the hadoop source tree. The subprojects (ozone/hdds) are part of the hadoop source tree but by default not compiled and not part of the official releases. To use it, you have to build a package by yourself and deploy a cluster.
Building Ozone
To build Ozone, please checkout the hadoop sources from github. Then checkout the trunk branch and build it.
mvn clean package -DskipTests=true -Dmaven.javadoc.skip=true -Pdist -Phdds -Dtar -DskipShade
skipShade is just to make compilation faster and not really required.
This will give you a tarball in your distribution directory. This is the tarball that can be used for deploying your hadoop cluster. Here is an example of the tarball that will be generated.
~/apache/hadoop/hadoop-dist/target/${project.version}.tar.gz
At this point we have an option to setup a physical cluster or run ozone via docker.
Running Ozone via Docker
This assumes that you have a running docker setup on the machine. Please run these following commands to see ozone in action.
Go to the directory where the docker compose files exist.
cd hadoop-dist/target/compose/ozone
Tell docker to start ozone, this will start a KSM, SCM and a single datanode in the background.
docker-compose up -d
Now let us run some work load against ozone, to do that we will run freon.
This will log into the datanode and run bash.
docker-compose exec datanode bash
Now you can run the ozone command shell or freon, the ozone load generator.
This is the command to run freon.
ozone freon -mode offline -validateWrites -numOfVolumes 1 -numOfBuckets 10 -numOfKeys 100
You can checkout the KSM UI to see the requests information.
http://localhost:9874/
If you need more datanode you can scale up:
docker-compose scale datanode=3
Running Ozone using a real cluster
Please proceed to setup a hadoop cluster by creating the hdfs-site.xml and other configuration files that are needed for your cluster.
Ozone Configuration
Ozone relies on its own configuration file called ozone-site.xml. It is
just for convenience and ease of management -- you can add these settings
to hdfs-site.xml, if you don't want to keep ozone settings separate.
This document refers to ozone-site.xml so that ozone settings are in one
place and not mingled with HDFS settings.
- ozone.enabled This is the most important setting for ozone.
Currently, Ozone is an opt-in subsystem of HDFS. By default, Ozone is
disabled. Setting this flag to
trueenables ozone in the HDFS cluster. Here is an example,
<property>
<name>ozone.enabled</name>
<value>True</value>
</property>
- ozone.metadata.dirs Ozone is designed with modern hardware in mind. It tries to use SSDs effectively. So users can specify where the metadata must reside. Usually you pick your fastest disk (SSD if you have them on your nodes). KSM, SCM and datanode will write the metadata to these disks. This is a required setting, if this is missing Ozone will fail to come up. Here is an example,
<property>
<name>ozone.metadata.dirs</name>
<value>/data/disk1/meta</value>
</property>
- ozone.scm.names Ozone is build on top of container framework. Storage container manager(SCM) is a distributed block service which is used by ozone and other storage services. This property allows datanodes to discover where SCM is, so that datanodes can send heartbeat to SCM. SCM is designed to be highly available and datanodes assume there are multiple instances of SCM which form a highly available ring. The HA feature of SCM is a work in progress. So we configure ozone.scm.names to be a single machine. Here is an example,
<property>
<name>ozone.scm.names</name>
<value>scm.hadoop.apache.org</value>
</property>
- ozone.scm.datanode.id Each datanode that speaks to SCM generates an ID just like HDFS. This is an optional setting. Please note: This path will be created by datanodes if it doesn't exist already. Here is an example,
<property>
<name>ozone.scm.datanode.id</name>
<value>/data/disk1/scm/meta/node/datanode.id</value>
</property>
- ozone.scm.block.client.address Storage Container Manager(SCM) offers a set of services that can be used to build a distributed storage system. One of the services offered is the block services. KSM and HDFS would use this service. This property describes where KSM can discover SCM's block service endpoint. There is corresponding ports etc, but assuming that we are using default ports, the server address is the only required field. Here is an example,
<property>
<name>ozone.scm.block.client.address</name>
<value>scm.hadoop.apache.org</value>
</property>
- ozone.ksm.address KSM server address. This is used by Ozonehandler and Ozone File System.
<property>
<name>ozone.ksm.address</name>
<value>ksm.hadoop.apache.org</value>
</property>
- dfs.datanode.plugin Datanode service plugins: the container manager part of ozone is running inside the datanode as a service plugin. To activate ozone you should define the service plugin implementation class. Important It should be added to the hdfs-site.xml as the plugin should be activated as part of the normal HDFS Datanode bootstrap.
<property>
<name>dfs.datanode.plugins</name>
<value>org.apache.hadoop.ozone.HddsDatanodeService</value>
</property>
Here is a quick summary of settings needed by Ozone.
| Setting | Value | Comment |
|---|---|---|
| ozone.enabled | True | This enables SCM and containers in HDFS cluster. |
| ozone.metadata.dirs | file path | The metadata will be stored here. |
| ozone.scm.names | SCM server name | Hostname:port or or IP:port address of SCM. |
| ozone.scm.block.client.address | SCM server name and port | Used by services like KSM |
| ozone.scm.client.address | SCM server name and port | Used by client side |
| ozone.scm.datanode.address | SCM server name and port | Used by datanode to talk to SCM |
| ozone.ksm.address | KSM server name | Used by Ozone handler and Ozone file system. |
Here is a working example ofozone-site.xml.
<?xml version="1.0" encoding="UTF-8"?>
<?xml-stylesheet type="text/xsl" href="configuration.xsl"?>
<configuration>
<property>
<name>ozone.enabled</name>
<value>True</value>
</property>
<property>
<name>ozone.metadata.dirs</name>
<value>/data/disk1/ozone/meta</value>
</property>
<property>
<name>ozone.scm.names</name>
<value>127.0.0.1</value>
</property>
<property>
<name>ozone.scm.client.address</name>
<value>127.0.0.1:9860</value>
</property>
<property>
<name>ozone.scm.block.client.address</name>
<value>127.0.0.1:9863</value>
</property>
<property>
<name>ozone.scm.datanode.address</name>
<value>127.0.0.1:9861</value>
</property>
<property>
<name>ozone.ksm.address</name>
<value>127.0.0.1:9874</value>
</property>
</configuration>
And don't forget to enable the datanode component with adding the following configuration to the hdfs-site.xml:
<property>
<name>dfs.datanode.plugins</name>
<value>org.apache.hadoop.ozone.HddsDatanodeService</value>
</property>
Starting Ozone
Ozone is designed to run concurrently with HDFS. The simplest way to start
HDFS is to run start-dfs.sh from the
$HADOOP/sbin/start-dfs.sh. Once HDFS
is running, please verify it is fully functional by running some commands like
- ./hdfs dfs -mkdir /usr
- ./hdfs dfs -ls /
Once you are sure that HDFS is running, start Ozone. To start ozone, you need to start SCM and KSM. Currently we assume that both KSM and SCM is running on the same node, this will change in future.
The first time you bring up Ozone, SCM must be initialized.
./ozone scm -init
Start SCM.
./ozone --daemon start scm
Once SCM gets started, KSM must be initialized.
./ozone ksm -createObjectStore
Start KSM.
./ozone --daemon start ksm
if you would like to start HDFS and Ozone together, you can do that by running a single command.
$HADOOP/sbin/start-ozone.sh
This command will start HDFS and then start the ozone components.
Once you have ozone running you can use these ozone shell commands to create a volume, bucket and keys.
Diagnosing issues
Ozone tries not to pollute the existing HDFS streams of configuration and
logging. So ozone logs are by default configured to be written to a file
called ozone.log. This is controlled by the settings in log4j.properties
file in the hadoop configuration directory.
Here is the log4j properties that are added by ozone.
#
# Add a logger for ozone that is separate from the Datanode.
#
#log4j.debug=true
log4j.logger.org.apache.hadoop.ozone=DEBUG,OZONE,FILE
# Do not log into datanode logs. Remove this line to have single log.
log4j.additivity.org.apache.hadoop.ozone=false
# For development purposes, log both to console and log file.
log4j.appender.OZONE=org.apache.log4j.ConsoleAppender
log4j.appender.OZONE.Threshold=info
log4j.appender.OZONE.layout=org.apache.log4j.PatternLayout
log4j.appender.OZONE.layout.ConversionPattern=%d{ISO8601} [%t] %-5p \
%X{component} %X{function} %X{resource} %X{user} %X{request} - %m%n
# Real ozone logger that writes to ozone.log
log4j.appender.FILE=org.apache.log4j.DailyRollingFileAppender
log4j.appender.FILE.File=${hadoop.log.dir}/ozone.log
log4j.appender.FILE.Threshold=debug
log4j.appender.FILE.layout=org.apache.log4j.PatternLayout
log4j.appender.FILE.layout.ConversionPattern=%d{ISO8601} [%t] %-5p \
(%F:%L) %X{function} %X{resource} %X{user} %X{request} - \
%m%n
If you would like to have a single datanode log instead of ozone stuff getting written to ozone.log, please remove this line or set this to true.
log4j.additivity.org.apache.hadoop.ozone=false
On the SCM/KSM side, you will be able to see
hadoop-hdfs-ksm-hostname.loghadoop-hdfs-scm-hostname.log
Please file any issues you see under the related issues: