I also had this problem. I did something wrong with my 8gb SanDisk Flash drive and it was showing 6gb as Allocated and 2gb as unallocated. When I was doing the right click on unallocated drive it was not showing any option to allocate.
After 1 hr search on the internet and downloaded so many software to fix the issue, I found the solution to get back my 8gb flash drive. Here is the solution:
1. Download the Lexar tool and extract to your PC
2. Click on the 'Non-Active' radio button at the bottom of the window
3. Now click on the 'Format' button
4. Remove and insert back of your Flash drive and you're done :o)
I hope this will help you to get back your Flash drive in original capacity.
1. Download the Lexar tool and extract to your PC from following link
2. Click on the ‘Non-Active’ radio button at the bottom of the window
3. Now click on the ‘Format’ button
4. Remove and insert back of your Flash drive
5. Go back to disc management and reformat the flash drive again and you will get the whole space again
If BootIt refuses to work do this:
Right click “computer” and click manage. Click “disk management”, then click your drive. Right click the affected partition (or whatever that empty space is) and click properties. Then go to the “tools” tab, and under “error checking” click “check now”. After it does this, reformat the drive, and you should have all of your storage back.