Using to manage HDFS HA You can use to configure your cluster for HDFS HA and automatic failover. Enabling HDFS HAAn HDFS high availability (HA) cluster uses two NameNodes -- an active NameNode and a standby NameNode. Only one NameNode can be active at any point in time.Prerequisites for enabling HDFS HA usingThere are certain prerequisites that your cluster must satisfy before HDFS HA can be enabled using .Enabling High Availability and automatic failoverYou can use to configure your cluster for HDFS HA and automatic failover. In , HA is implemented using Quorum-based storage. Quorum-based storage relies upon a set of JournalNodes, each of which maintains a local edits directory that logs the modifications to the namespace metadata. Enabling HA enables automatic failover as part of the same command.Disabling and redeploying HDFS HAWhen you disable HDFS HA, ensures that one NameNode is active, and saves the namespace. Then it stops the standby NameNode, creates a Secondary NameNode, removes the standby NameNode role, and restarts all the HDFS services.Configuring other components to use HDFS HAYou can use the HDFS high availability NameNodes with other components of .Changing a nameservice name for Highly Available HDFS usingBased on your requirements, you can change a nameservice name for a cluster that has HDFS HA configured.Manually failing over to the standby NameNodeIf you are running a HDFS service with HA enabled, you can manually cause the active NameNode to failover to the standby NameNode. This is useful for planned downtime—for hardware changes, configuration changes, or software upgrades of your primary host.Additional HDFS haadmin commands to administer the clusterAfter your HA NameNodes are configured and started, you will have access to some additional commands to administer your HA HDFS cluster.Turning safe mode on HA NameNodesYou can use the applicable dfsadmin command options to turn safe mode on for a single or both the active and standby NameNodes. Converting from an NFS-mounted shared edits directory to Quorum-Based StorageConverting a HA configuration from using an NFS-mounted shared edits directory to Quorum-based storage involves disabling the current HA configuration then enabling HA using Quorum-based storage.Parent topic: Configuring HDFS High Availability
