Home > Storage > PowerScale (Isilon) > Product Documentation > Management and Migration > Dell PowerScale: Non-Disruptive Upgrade Best Practices > What is NDU
NDU is a framework which is introduced in OneFS 8.0 to provide better control and predictability to the upgrade process.
From a user perspective, the goal is to provide a seamless and robust upgrade process which is non- disruptive to normal business workflows.
At a high level, the NDU framework implements a state machine, which means at any given time, the PowerScale cluster is at one of the following states:
NDU supports the state's transition through some user actions. For details of the NDU state machine and its transition, refer to Pre-upgrade check.
At the low level, the NDU framework is implemented by a controlling Supervisor process and a servant Agent daemon process on every PowerScale node.
Note: NDU framework is not only used for OneFS upgrade, it is applied to patch and node firmware upgrade as well. This chapter will only focus on the OneFS upgrade. For patch upgrade, see the section Patch upgrade.