The upgrade of a distributed switch causes the hosts and virtual machines attached to the switch to experience a brief downtime. Please perform the activity during your maintenance window.
Note:
To be able to restore the connectivity of the virtual machines and VMkernel adapters if the upgrade fails, back up the configuration of the distributed switch.
If your current VDS version is 6.6 or later, then you might not experience any downtime while upgrading the switches to a later version.
Caution: After you upgrade the vSphere Distributed Switch, you cannot revert it to an earlier version. You also cannot add ESXi hosts that are running an earlier version than the new version of the switch