If you want to defrag your hard drives in Windows 8 you can still use your O&O defrag software or you use the built-in tools. Works exactly like it did in Windows 7 (last update: Developer Preview)
Using The Built In Windows Defrag Tool
1. Step Open the Windows 8 explorer
2. Step Right-click on the hard drive that you think is fragmented and click on Properties
3. Step Go to the Tools tab and click on Optimize now at the bottom:
4. Step The built-in Windows 8 defragmentation program opens. By default, Windows 8 schedules a weekly disk defragmentation. So, even if you have not defragmented your disk, Windows 8 might have done it for you and your disk might not even require a defragmentation.
5. Step Select the drive that you want to analyze and click the Analyze button
Windows 8 will analyze your hard drives and will let you know if you should defragment it.
If you want to defrag Windows 8 professionally you can also try tools like O&O Defrag the leading defrag software for Windows PC’s. Windows 8 supports most if not all Windows 7 defrag tools.