Before You Upgrade the Operating System

1. Log in to the Cloudera Manager Admin Console.
2. From the All Hosts page, select the host that you wish to upgrade. Cloudera recommends that you upgrade only one host at a time.
3. Select Begin Maintenance (Suppress Alerts/Decommission) from the Actions menu.
4. Select Host Decommission from the Actions menu. Any roles that do not require decommission will be skipped.
5. If the operating system upgrade procedure takes less than 30 minutes per node, you do not need to decommission the DataNode.

   If the Cloudera Manager and CDH version are both 5.14 or greater, you can also choose the Take DataNode Offline feature.

   If in doubt, decommission the roles.

   • When a DataNode is decommissioned, the NameNode ensures that every block from the DataNode is still available across the cluster as specified by the replication factor. This procedure involves copying blocks off the DataNode in small batches. In cases where a DataNode has several thousand blocks, decommissioning takes several hours.
   • When a DataNode is turned off without being decommissioned:
     • The NameNode marks the DataNode as dead after a default of 10m 30s (controlled by the dfs.heartbeat.interval and dfs.heartbeat.recheck.interval configuration properties).
     • The NameNode schedules the missing replicas to be placed on other DataNodes.
     • When the DataNode comes back online and reports to the NameNode, the NameNode schedules blocks to be copied to it while other nodes are decommissioned or when new files are written to HDFS.
   • You can also speed up the decommissioning of a DataNode by increasing values for these properties:
     • dfs.max-repl-streams: The number of simultaneous streams used to copy data.
     • dfs.balance.bandwidthPerSec: The maximum amount of bandwidth that each DataNode can utilize for balancing, in bytes per second.
     • dfs.namenode.replication.work.multiplier.per.iteration: NameNode configuration requiring a restart, defaults to 2 but can be raised to 10 or higher.

       This determines the total amount of block transfers to begin in parallel at a DataNode for replication, when such a command list is being sent over a DataNode heartbeat by the NameNode. The actual number is obtained by multiplying this value by the total number of live nodes in the cluster. The result number is the number of blocks to transfer immediately, per DataNode heartbeat.

6. Once that is completed, select the same host again and choose Stop Roles on Hosts.

Use the operating system upgrade procedures provided by your operating system vendor (for example: RedHat or Ubuntu) to download their software and perform the operating system upgrade.