How to "Clean" or "Clean All" a Disk with the Diskpart Command

Follow the Steps:-

1. In Windows 7, open an command prompt, or a command prompt at boot.

OR

2. In Windows 8 and 8.1, open an command prompt, or a command prompt at boot.

A) Press the Windows + R keys to open the Run dialog, type compmgmt.msc, and press Enter.

B) If prompted by UAC, click/tap on Yes.

C) Click/tap on Disk Management in the left pane, and make note of the disk #
      in the middle pane of the disk that you want to clean or clean all.

NOTE: For example, I would use Disk 1 if I wanted to use clean or clean all on my USB key drive


3. In the command prompt, type diskpart and press Enter. (see screenshot below)

4. In the command prompt, type list disk and press Enter. (see screenshot below) 

NOTE: This will give you a list of disk numbers to select from.

5. In the command prompt, type select disk # and press Enter. (see screenshot below)

NOTE: You would substitute # for the disk number listed that you want to use clean or clean all on. For example, I want to use one of them on Disk 1 (from step 1) for my USB key drive, so I would type select disk 1 and press Enter.

6. If the status of the selected disk # (ex: Disk 1) shows as Offline, type online disk, and press Enter to make it online. 

7. Do either step 8 or 9 below for which command you would like to use.


8. To Use the Clean Diskpart Command
NOTE: (Recommended) See the green INFO box at the top of the tutorial for more information about this command. This command will wipe the HDD quickly.

A) In the  command prompt, type clean, press Enter, and go to step 10 below.
NOTE: This will not take long to finish. Think of it as being like a quick format.

9. To Use the Clean All Diskpart Command 
NOTE: See the green INFO box at the top of the tutorial for more information about this command. This command will wipe the HDD, and perform a secure erase. "Clean All" takes about an hour per 320 GB to finish running. It's best to only use this command if you wanted to help make sure that the data on the HDD cannot be recovered say when giving or selling the HDD to another person.

A) In the command prompt, type clean all, and press Enter, and go to step 10 below. You will see the command prompt below as is until the "clean all" command is finished.

NOTE: This will take quite some time (several hours or more) to finish depending on how large the disk is since it is writing over each and every sector on it to zero. Think of it as being like a full or low level format.

10. When finished, in the command prompt, type exit and press Enter. Close the elevated command prompt.

11. The disk will be left as unallocated space. 

12. You will now need to create a new partition or volume on the disk to be able to use it again.

Done:)