chkdsk /? will give you all flags. Normally all you need to do is a chkdsk /f
Which of these new options checks all sectors for bad sectors, such as chkdsk /r did?
I've just used chkdsk /r for the first time and it took about 5 hours to check a 2T hard drive! It stuck at a low percentage then suddenly completed with no errors. Use chkdsk /r /v and it will tell you more about what it is doing.