@vinothkaliaperumal-2643 Welcome to Microsoft Q&A Forum, Thank you for posting your query here!
Firstly, There is No downtime if we resize the ANF volume. New size gets automatically reflected .
How to update this in Linux OS level : We need to unmount and mount it back because the OS does not know what happened at the NetApp storage level.
Please let us know if you have any further queries. I’m happy to assist you further.
Please do not forget to "Accept the answer” and “up-vote” wherever the information provided helps you, this can be beneficial to other community members.