Removing Ozone DataNodes from the cluster

You can remove Ozone DataNodes from the CDP cluster in a controlled manner using Cloudera Manager for performing maintenance operations. If you want to remove the DataNodes permanently or for an unknown duration, you can decommission them. If you want to make the DataNodes unavailable for a short period of time, such as, for a few days or hours, you can place them in offline mode.

When you initiate the process of decommissioning a DataNode, Ozone automatically ensures that all the storage containers on that DataNode have an additional copy created on another DataNode before the decommission completes. Similarly, when you initiate the process of placing a DataNode in offline mode, Ozone ensures that at least two copies of the DataNode's storage containers are present on other nodes before the particular DataNode enters offline mode.

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Before a DataNode enters offline mode, you can reduce the minimum number of online copies of the storage container from two to one. This process reduces the time to complete the offline mode operation. However, the process increases the risk of data becoming temporarily unavailable if another DataNode fails.
For details on how to reduce the minimum number of storage container copies, see Configuring the number of storage container copies for a DataNode.
Ozone does not specify any upper limit on the number of DataNodes you can simultaneously decommission or place in offline mode. However, there must be enough space on the cluster to hold the additional storage containers. Otherwise, the DataNodes cannot complete the decommissioning or offline mode processes.

You can also recommission a DataNode that is already decommissioned or placed in offline mode. When you recommission such a DataNode, Ozone automatically removes any excess containers created during the decommission or offline process.