How to fix HDD failure on a MacBook Pro?
The error File system check exit code is 8 indicates you have an unrecoverable file system read error.

This can be due to either or both of the following:


Corrupted file system
Failing/failed hardware


If it's a just a file system problem, you can try the following:


run First Aid multiple times to see if the problem gets fixed
wipe your drive (format it) and reinstall macOS


Obviously, if the first option doesn't fix the problem, your next option is to format and reinstall.

If it's a hardware issue, your best bet would be to replace the failing drive with a new one.  Your MacBook Pro (MacBookPro7,1) is a Mid-2010 model which means it's a 7 year old drive (if it hasn't been replaced) which is well beyond the lifespan of spinning hard drives.  At this point, I would recommend upgrading to an SSD and even maxing out the memory for best performance.

While I agree with @klanomath that it could be the SATA cable, it's not the most likely culprit given the age of the laptop and drive.  My money is on a failed hard drive.  However, a replacement SATA cable is fairly inexpensive part to replace and if you decide to go that route, it won't be an expensive investment.