Can bad SATA cables be responsible for bandwidth slowdown, disconnects while showing 100% in Task Manager? How does the 100% even work?

[CyJackX]

My system is from 2014 btw; AFAIK my PSU is enough? It's 650W, 4770k, 32GB ram, GTX970, 2 SSDs, 4 HDDs.
At any given time at least one of the HDDs will be disconnected.
I thought maybe it was a bad SATA cable, so I swapped some around and then the ones that were working swapped, but then it seems like they swapped back! And sometimes the SSD even disconnects. One of the problem drives will show 100% on CrystalDisk yet show double digit transfer speeds. I ran CHKDSK on one of them and nothing turned up.

How does 100% Disk Utilization on Task Manager even work? 100% according to what internal metric? Because I'll try to play a movie off of a drive and it'll be fine and Disk utilization will be low, and then it will stutter as it spikes to 100%, even if the read speed hasn't increased.

 

[mwroobel]

What do the SMART numbers from all attached drives show? Is it all the drives hooked to a particular controller that are a problem (PCH connected, Third party connected) or is it all the drives randomly? Cables of course can cause problems, but so can bad power. If you have another power supply to try, do that first. Unfortunately, it is going to be a trial and error until you get to the problem, which could be almost anything in your system from power to cables to the motherboard and its components.