Search for files in external storage in Finder (and if possible, Spotlight as well) I have an external drive connected to my computer, as well as a home server.

I'm trying to search for a file that is on the server, but when I do a finder search, it only looks into the internal drive. I've tried it with my external drive, and same thing happens -- it does not look there.
You can add the Volume to your Spotlight index.

Go to System Preferences then to Spotlight.


Click on the Privacy tab Click the + button and browse to your
external drive to add it
Now, remove the drive you just added by selecting it and clicking
the minus "-" button. (Yes, I know, crazy right! But this tells
Spotlight that the Volume exists.)
Close Spotlight Preferences.


Source: Apple Support - Spotlight: How to re-index folders or volumes.