The top one only using like 0.2 MB/s like the rest of the other one thoughCtrl + Alt + Del > open Task Manager > Processes tab > Then click the Disk tab.
The top one will be what is using all of your drive resources.
In the Performance tab the resource monitor will give you more info on disk activity.
Open Resource Monitor - Disk tab - Disk Activity section and look for processes with most read/write (can sort by column total).
Expand File column to get info about file being read/written.
Post screenshot (upload to imgur.com and post link)
It would look similar to this:
[//spoiler]
During defragmenting disk activity will be high. This is normal.
Wait until it finishes.