hadoop/hadoop-hdds/docs/content/Settings.md

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If you are feeling adventurous, you can setup ozone in a real cluster. Setting up a real cluster requires us to understand the components of Ozone. Ozone is designed to work concurrently with HDFS. However, Ozone is also capable of running independently. The components of ozone are the same in both approaches.

Ozone Components

1. Ozone Manager - Is the server that is in charge of the namespace of Ozone. Ozone Manager is responsible for all volume, bucket and key operations.
2. Storage Container Manager - Acts as the block manager. Ozone Manager requests blocks from SCM, to which clients can write data.
3. Datanodes - Ozone data node code runs inside the HDFS datanode or in the independent deployment case runs an ozone datanode daemon.

Setting up an Ozone only cluster

• Please untar the ozone- to the directory where you are going to run Ozone from. We need Ozone jars on all machines in the cluster. So you need to do this on all machines in the cluster.

• Ozone relies on a configuration file called ozone-site.xml. To generate a template that you can replace with proper values, please run the following command. This will generate a template called ozone-site.xml at the specified path (directory).

{{< highlight bash >}} ozone genconf {{< /highlight >}}

Let us look at the settings inside the generated file (ozone-site.xml) and how they control ozone. Once the right values are defined, this file needs to be copied to ozone directory/etc/hadoop.

• ozone.enabled This is the most critical setting for ozone. Ozone is a work in progress and users have to enable this service explicitly. By default, Ozone is disabled. Setting this flag to true enables ozone in the HDFS or Ozone cluster.

Here is an example,

{{< highlight xml >}} ozone.enabled true {{< /highlight >}}

• ozone.metadata.dirs Allows Administrators to specify where the metadata must reside. Usually you pick your fastest disk (SSD if you have them on your nodes). OzoneManager, SCM and datanode will write the metadata to this path. This is a required setting, if this is missing Ozone will fail to come up.

  Here is an example,

{{< highlight xml >}} ozone.metadata.dirs /data/disk1/meta {{< /highlight >}}

• ozone.scm.names Storage container manager(SCM) is a distributed block service which is used by ozone. This property allows data nodes to discover SCM's address. Data nodes send heartbeat to SCM. Until HA feature is complete, we configure ozone.scm.names to be a single machine.

Here is an example,

{{< highlight xml >}} ozone.scm.names scm.hadoop.apache.org {{< /highlight >}}

• ozone.scm.datanode.id.dir Data nodes generate a Unique ID called Datanode ID. This identity is written to the file datanode.id in a directory specified by this path. Data nodes will create this path if it doesn't exist already.

Here is an example, {{< highlight xml >}} ozone.scm.datanode.id.dir /data/disk1/meta/node/datanode.id {{< /highlight >}}

• ozone.om.address OM server address. This is used by OzoneClient and Ozone File System.

Here is an example, {{< highlight xml >}} ozone.om.address ozonemanager.hadoop.apache.org {{< /highlight >}}

Ozone Settings Summary

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 IP:port address of SCM.
ozone.scm.block.client.address	SCM server name and port	Used by services like OM
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.om.address	OM server name	Used by Ozone handler and Ozone file system.