I have my Wordpress multisite installed in /var/www/example.com/u/
I created a block-storage called storage and it is mounted under /mnt/storage/, this contains a folder called /uploads.
In my Wordpress wp-config.php ...
I would recommend first copying your current uploads folder to your new location:
cp -r /var/www/example.com/u/wp-content/uploads/* /mnt/storage/uploads
That way you would make sure that your existing images ...
First off, I just setup a debian server with LEMP.
I have a very special setup, which is one Wordpress installation in the root folder, and a Wordpress Multisite network which is installed in a subfolder called "/u".