By default, the "Media" directory is on my "sda", but I want to add another HDD and move "Media" directory to it. Which line of configuration must be change?
let's example your site url is : test.com
and you set media url to : test2.com
you need to upload all files into test2.com
hope it will help you.
Easiest thing to do is move the media directory to your other partition, then symlink media in your Magento root directory to the new location.
For example, if your Magento root in in:
and your new media directory is:
ln -s /home2/xxx/media /home/xxx/public_html/media