4. Configuring Archival Storage

Use the following steps to configure archival storage:

1. Shut Down the DataNode

Shut down the DataNode using the applicable commands in the Controlling HDP Services Manually section of the HDP Reference Guide.

2. Assign the ARCHIVE Storage Type to the DataNode

To assign the ARCHIVE storage type to a DataNode, use the dfs.datanode.data.dir property in the/etc/hadoop/conf/hdfs-site.xml file.

The dfs.datanode.data.dir property determines where on the local filesystem a DataNode should store its blocks.

If you specify a comma-delimited list of directories, data will be stored in all named directories, typically on different devices. Directories that do not exist are ignored. You can specify that each directory resides on a different type of storage: DISK, SSD, ARCHIVE, or RAM_DISK.

To specify a DataNode as DISK storage, use a local file system path. For example:

<property>
 <name>dfs.datanode.data.dir</name>
 <value>[DISK]file:///grid/1/tmp/data_trunk</value>
</property>

To specify a DataNode as ARCHIVE storage, insert [ARCHIVE] at the beginning of the local file system path. For example:

<property>
 <name>dfs.datanode.data.dir</name>
 <value>[ARCHIVE]file:///grid/1/tmp/data_trunk</value>
</property>

3. Set or Get Storage Policies

Set a storage policy on a file or a directory:

hdfs dfsadmin -setStoragePolicy <path> <policyName>

Arguments:

Example:

hdfs dfsadmin -setStoragePolicy /cold1 COLD

Get the storage policy of a file or a directory:

hdfs dfsadmin -getStoragePolicy <path>

Argument:

Example:

hdfs dfsadmin -getStoragePolicy /cold1 

4. Start the DataNode

Start the DataNode using the applicable commands in the Controlling HDP Services Manually section of the HDP Reference Guide.

5. Using Mover to Apply Storage Policies

When you update a storage policy setting on a file or directory, the new policy is not automatically enforced. You must use the HDFS mover data migration tool to actually move blocks as specified by the new storage policy.

The mover data migration tool scans the specified files in HDFS and checks to see if the block placement satisfies the storage policy. For the blocks that violate the storage policy, it moves the replicas to a different storage type in order to fulfill the storage policy requirements.

Command:

hdfs mover [-p <files/dirs> | -f <local file name>] 

Arguments:

	Note
	Note that when both -p and -f options are omitted, the default path is the root directory.

Example:

hdfs mover /cold1/testfile