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Cluster expansion

This guide covers common ways to grow capacity: new Datanodes, extra disks on existing Datanodes, and more memory (heap) for a Datanode. These operations are supported; Ozone picks up new nodes and storage through normal Datanode registration and heartbeat metadata—no separate “sync” step is required beyond correct configuration and restart where noted.

Adding capacity does not immediately redistribute existing data. New writes use the expanded cluster; to spread load or disk usage, use the balancers linked below.

Add a new Datanode​

  1. Prepare the host (OS, Java, network, users/permissions) and install Ozone binaries—same as any new node. See the bare-metal installation guide and Installing Ozone binaries.

  2. Copy or generate ozone-site.xml (and related config) so this node matches the cluster’s OM/SCM addresses, security settings, and storage layout conventions.

  3. Start the Datanode on the new host:

    ozone --daemon start datanode

    For a full startup order and optional scripts, see Starting and Stopping the Ozone Cluster.

After the Datanode registers with SCM, its capacity is available for new containers and replicas.

Balance load across Datanodes​

To move existing closed containers toward an even utilization of the cluster, run the Container Balancer after expansion.

Add a disk to an existing Datanode​

  1. Install the disk, format it, and mount it on the host.
  2. Ensure the Ozone process user can read/write the mount (ownership and permissions).
  3. Append the new mount path to hdds.datanode.dir in ozone-site.xml (comma-separated list). See the configuration appendix for property details.
  4. Restart the Datanode so it picks up the new volume.

SCM learns the added capacity through the Datanode’s storage reports.

Balance traffic across disks​

To shift work between disks on the same Datanode, use the Disk Balancer.

Increase Datanode memory (heap)​

You do not need Ozone configuration keys to use additional RAM on the host; the process can use what the OS provides.

To raise the Datanode Java heap explicitly, set the environment (for example in the service environment file or before launch), then restart the Datanode:

  • OZONE_HEAPSIZE_MAX — sets the maximum heap (-Xmx).
  • OZONE_DATANODE_OPTS — additional JVM options for Datanodes.

See Environment variables for descriptions and examples.

CPU: Extra vCPUs or sockets do not require Ozone-specific settings; the running Datanode benefits after restart if you also change JVM or service limits at the OS level.