...
Plan upgrade impacts — Review and plan for this release's upgrade impacts and the impacts for each of the releases since the currently running version. For Swarm 9 impacts, see Swarm Storage 9 Releases.
No volume retires — Do not start any elective volume retirements during the upgrade. Wait until the upgrade is complete before initiating any retires, or verify they are complete before upgrading.
Choose the reboot type — Swarm supports rolling upgrades (a single cluster running mixed versions during the upgrade process) and requires no data conversion unless specifically noted for a particular release. Upgrades are performed without scheduling an outage or bringing down the cluster. Restart the swarm nodes one at a time with the new version and the cluster continues serving applications during the upgrade process.
Rolling upgrade: Reboot one node at a time and wait for its status to show as "OK" in the UI before rebooting the next node.
Alternative: Reboot the entire cluster at once after the software on all USB flash drives or the centralized configuration location has been updated.
Follow the Upgrade Path, below.
Review the Application and Configuration Guidance.
...