Nondisruptive upgrades on these fabric switches disrupts the control plane for not more than 80 seconds. The software upgrade might be disruptive if the upgrade progresses beyond when it can be stopped gracefully or if a failure occurs.
https://www.cisco.com/c/en/us/td/docs/switches/datacenter/mds9000/sw/6_2/upgrade/guides/nx- os/upgrade.html