If you have a Mini 9 then most likely Hibernate was disabled when you set things up. You can check looking at a few things from terminal.
Do a: pmset -g
If hibernate is on then hibernamemode is 3. If off then it's 0
To see if you have a hibernate file do a: ls -la /var/vm
If you see a sleepimage file then it is eating up space. The swapfile0 is normal. Don't touch this file.
You can use DellEFI or NetbookInstaller to disable Hibernate if it is on. That will automatically issue the sudo pmset -a hibernatemode=0 and will also do a sudo rm /var/vm/sleepimage.