What is the hard drive nodebb?
Server Parameters my server:
2 GB RAM
SSD 10 GB
Local Raid 10
now occupies more than 5GB forum wanted to know how much is enough for me that drive and part of the database itself here is the way a lot of mongo DB
NodeBB itself with all of its dependencies installed takes up maybs ~200mb. The database itself takes up as much as shown in that page above, and scales up with the amount of content in your forum, obviously.
You'll probably want more than 10GB, and that's a miniscule amount to handle your site data and your operating system.
If your site contains a lot of user data such as images you may want to consider using a plugin that would offload that content to a 3rd party provider such as Imgur or Amazon S3. Plugins exist for NodeBB for both of those services.