Windows 7: HDD losing space when defraging

Had 31.9 GB when I started defrag, only 5.6 afterwards

Hello RICSHA62 and welcome to Seven Forums.

It's possible that temporary files were created during the defrag session. It's also possible that restore point(s) were created and new files were created by VSS (volume shadow storage). I'd run Disk Cleanup (option 3, this tutorial.) I'd also disable Hibernation and delete hibernation files if you don't use the hibernation feature (option 9.) Windows 7 sets aside 10% of your disk spce for System Protection. I'd consider reducing that to perhaps 5% (option 11.) Finally, I'd delete unwanted/unneeded shadow copies (option 19.)

These steps should give you back a good chunk of disk space. Then I'd go through all the other options to see if there isn't some more disk space that you can regain.

Hard Disk Space - Free Up and Recover

Thank you marsmimar.
Did everything suggested and gained 58.7 GB.

That's fantatic news! Thanks for posting back.