Configuring the Storage Policy for the Write-Ahead Log (WAL)

In CDH 5.7.0 and higher, you can configure the preferred HDFS storage policy for HBase's write-ahead log (WAL) replicas. This feature allows you to tune HBase's use of SSDs to your available resources and the demands of your workload.

These instructions assume that you have followed the instructions in Configuring Storage Directories for DataNodes and that your cluster has SSD storage available to HBase. If HDFS is not configured to use SSDs, these configuration changes will have no effect on HBase. The following policies are available:
  • NONE: no preference about where the replicas are written.
  • ONE_SSD: place one replica on SSD storage and the remaining replicas in default storage. This allows you to derive some benefit from SSD storage even if it is a scarce resource in your cluster.
  • ALL_SSD: place all replicas on SSD storage.

Configuring the Storage Policy for WALs Using Cloudera Manager

Minimum Required Role: Full Administrator

  1. Go to the HBase service.
  2. Click the Configuration tab.
  3. Search for the property WAL HSM Storage Policy.
  4. Select your desired storage policy.
  5. Save your changes. Restart all HBase roles.
Changes will take effect after the next major compaction.

Configuring the Storage Policy for WALs Using the Command Line

Paste the following XML into hbase-site.xml. Uncomment the <value> line that corresponds to your desired storage policy. 
<property>
  <name>hbase.wal.storage.policy</name>
  <value>NONE</value>
  <!--<value>ONE_SSD</value>-->
  <!--<value>ALL_SSD</value>-->
</property>

Restart HBase. Changes will take effect for a given region during its next major compaction.