Home > Storage > PowerScale (Isilon) > Product Documentation > Management and Migration > Dell PowerScale: Non-Disruptive Upgrade Best Practices > FTP behavior and configuration consideration
FTP is a stateful protocol which means PowerScale should keep the session state between the client and itself. For this reason, the recommendation is to use a static IP pool. The IP will not failover or failback during the PowerScale node reboot. The client has to wait for FTP serviceability to resume on the node that it is connected to. In this case, using SmartConnect Service IPs (SSIP) can help minimize the impact. SSIP is implemented by a way of DNS delegation and it can help to redirect the request to the right PowerScale nodes which are still alive. However, if the rolling upgrade reboot happens in the middle of file transmission, the transmission will get stopped with errors and need to be manually re-establish the connection. The recommendation is as below:
Note: With all the recommendations above, the OneFS upgrade process still provides a disruptive upgrade. But it can dramatically minimize the impact.