Q & A: howto use another space in my system for storage?

I have a Big empty secondary 1TB drive. I need to point one of my domains to the secondary drive instead of the default /var/www/vhosts/somedomain.com/
Do you know how I can do that?

you can do that like:

mv /var/www/vhosts/yourftpusername /var/www/vhosts/yourftpusername2
ln -s /your/target/empty/drive/path /var/www/vhosts/yourftpusername
mv /var/www/vhosts/yourftpusername2/* /var/www/vhosts/yourftpusername/
chown -Rvf vsftpd /var/www/vhosts/yourftpusername

This was simple linux so-called "symlinking".
I did not tested it but should work.

the idea is:
move your original data to a new name,
symlink your empty space to your original path
move your original data to your new symlink
make it ftp reachable (owned by vsftpd service)