Hard Disk Monitoring

Some of my new files on my 8TB hhd started to read very slowly, so I started to check out my hdd.

Shows 9% health: I started a surface read test which runs now for 21 hours and est 27 hours. Until like 75% it was fast and the estimated was 9 hour. It seems it reached a part on the disk that got very slow. At morning I left it with 77%, and after came back from work, it is on 79%. Also I hear some clicking from the hdd. How long shall I wait for this to finish?
What does this mean?
Shall I try the disk repair and/or the reinitialize after this?
Since the hdd already has lots of (around 16000) bad sectors that probably got handled by SMART, will it be able to quarantine/repair all these slow sectors after the 75%?

I still have the guarantee (24+12 month and this is just 14 month old hdd), so I guess I should take this back to the shop?

Depending on the amount of possible problems which currently not yet detected, the test may run for another several hours (or even days).

The purpose of the hard disk test is exactly to reveal possible problems - or confirm if the status is good/stable.
So until we pass a particular sector, we can't be sure how long it will take: if the sector is good, then the test will process quickly - but if a single sector fails, it may take longer time to proceed (as usually the drive attempts to recover, retry the operation, may attempt to reallocate: replace with spare sector and so. These all take time).

As you can see in the upper right area, each one block (small square) represents over 1 and half million sectors on this hard disk drive, so there are still over a TB to test.

But as you can see, really high amount of problems and bad sectors already detected on this hard disk and its health is already so low, so I'd see no point in further testing: if you have warranty, then please ask for warranty replacement, it is the best solution now.

Generally problems (even on a new hard disk) may remain undetected for very long time (even months/years) until we test the corresponding area (especially on a high capacity drive which may take long time to fill).
A similar case described on https://www.hdsentinel.com/hard_disk_ca ... ectors.php
showing a hard disk with problems on the end of the disk surface area (similar to yours).

This is why it is generally important to test even a new hard disk before using for real storage: exactly to reveal such issues - or confirm that the hard disk drive is working correctly and we can trust it, as described at
https://www.hdsentinel.com/faq.php#tests