First of All Lets see what is Disk Scan?
Disc scan is one of the protective feature of windows which runs to clean any cross-links or bad sectors that may be generated because of the improper shutdown of windows due to some reason. So, when ever you shutdown your system in some improper way ,the next time you boot your windows you will see scan disk running which you can stop by pressing an key on time.
But in some cases as experienced by some of the windows users, disk scan runs every time they reboot, this happens because of the following reasons:
1. Improper shutdown(most common).
2. External HDD or portable drive attached which causes scan disk to scan them at every reboot.
3. chkdsk was not allowed to be completed at the time of boot.
Above reasons are normally the most common reasons behind this problem, but none of them matches with your case then, you probably have a dirty volume on your hard drive which has some bad sectors which does not get repaired at the time of reboot.
So, at every reboot chkdsk tries to repair those dirty bits on those bad sectors on your hard drive in those specific partitions.
But, don’t worry as you can simply fix this problem of disc scanning at every reboot.
You need to do a manual chkdsk on all the partitions or physical hard drives.
1. Open start–>run and type cmd
2. Type chkntfs /x