Configuring Upgrade Domains
Upgrade Domains allow to group cluster hosts for optimal performance during restarts and upgrades.
Upgrade Domains enable faster cluster restarts, faster Cloudera Runtime upgrades, and seamless OS patching & hardware upgrades across large clusters. Upgrade Domains provide an alternative to the default HDFS block placement policy, distributing data across a set of hosts (potentially larger than a single rack) that Cloudera Manager can upgrade/restart at once without compromising service and data availability. When you select Upgrade Domains as the block placement policy, you also assign an Upgrade Domain group to each DataNode host. The NameNode uses these groups to distribute blocks when writing data, and to orchestrate rolling restarts and upgrades. This feature is useful for very large clusters, or for clusters where rolling restarts happen frequently.
For example, if HDFS is configured with the default replication factor of 3, the NameNode places the replica blocks on DataNode hosts in 3 different Upgrade Domains and on at least two different racks.