Not sure if I should post my question in superuser, but it looks like the most appropriate place among all StackExchange sites.

I have a 16GB Kingston DataTraveler USB drive. When I tried to use it this morning, it showed up nothing in there but yet its details showed that half of the capacity was in used. I tried it with OS X, Ubuntu, and Windows 7 and the results were the same. I tried to create a new folder and it worked. Apparently, the drive is working but somehow not showing my previously stored data. Note that I was still using the drive last night and there wasn't any problems.

Following @rob's suggestion, du -h gave me:

16K 
./.Trashes 960K 
./.Spotlight-V100/Store-V1/Stores/2620683B-A38B-42F4-A247-45CAF4826ADE 976K ./.Spotlight-V100/Store-V1/Stores 1008K 
./.Spotlight-V100/Store-V1 1.0M 
./.Spotlight-V100 1.1M

And, df -h gave me:

/dev/sdb1 15G 7.9G 7.1G 53% /media/KINGSTON 

Confirming what I reported.

Anyone got a clue/answer to this issue? Thanks.