Linux does a great job of checking the local file systems every once in a while to make sure there is no corruption. Unfortunately, this luxury does not extend to removable drives. It will give you a warning (file system unchecked for so many days), but will do nothing about it. That is why I recommend doing a manual check on your external drives from time to time.
If you run fsck with the default options, it will not display any indication of progress, and that can get annoying if you have a large drive and don’t know how much longer you’ll have to wait. But there is a simple solution to this, I only wish I had taken the time to read the man page earlier:
fsck -C /dev/sda5
that will display a nice progress indicator while scanning (works only for ext2/ext3).