Hi,
I am using mongodb 3.4.4,
Machine got restarted due to power fluctuation. After that mongodb server was not starting at all.
When devugged we found that one of the .ns file is corrupted and due to that mongo is not starting.
After removing it from database directory mongo is starting.
Is there any way to repair that .ns file only?
We tried repairing whole data directory but no luck.
Thanks in advance…
Hello @Shivananda_Shiragavi ,
Welcome to The MongoDB Community Forums! 
MongoDB v3.4 was released in November 2016 and reached end of life in January 2020. Starting in version 4.2, MongoDB removes the deprecated MMAPv1 storage engine.
The possible way to restore .ns file is to restore from a recent backup.
I would recommend you to upgrade your version to at least MongoDB version 4.4 as it still comes under support till February 2024. Generally, upgrading the servers to the latest stable release is always recommended as it involves many new features, bug fixes and removed vulnerabilities.
Below you can find recent MongoDB releases with life cycle schedule
For upgrade procedure kindly refer below link
Regards,
Tarun