When USB flash disk isn't ejected properly and have an issue that your computer saying "you need to format" then following article will help. I had an USB comes with RAW disk and kept asking me to format. I read through all of the article and it fixed my issue. If USB HDD is containing important information then proceed with caution and if possible make a backup. http://html5.litten.com/updated-how-to-fix-external-disk-drive-suddenly-became-raw