I have not performed any profile testing of this yet, but what would the general consensus be on the advantages/disadvantages of resource loading from the hard disk using multiple threads vs one thread? Note. I am not talking about the main thread.

I would have thought that using more than one "other" thread to do the loading to be pointless because the HD cannot do 2 things at once, and therefore would surely only cause disk contention.

Not sure which way to go architecturally, appreciate any advice.

EDIT: Apologies, I meant to mean an SSD drive not a magnetic drive. Both are HD's to me, but I am more interested in the case of a system with a single SSD drive.

As pointed out in the comments one advantage of using multiple threads is that a large file load will not delay the presentation of a smaller for to the receiver of the thread loader. In my case, this is a big advantage, and so even if it costs a little perf to do it, having multiple threads is desirable.

I know there are no simple answers, but the real question I am asking is, what kind of performance % penalty would there be for making the parallel disk writes sequential (in the OS layer) as opposed to allowing only 1 resource loader thread? And what are the factors that drive this? I don't mean like platform, manufacturer etc. I mean technically, what aspects of the OS/HD interaction influence this penalty? (in theory).

FURTHER EDIT: My exact use case are texture loading threads which only exist to load from HD and then "pass" them on to opengl, so there is minimal "computation in the threads (maybe some type conversion etc). In this case, the thread would spend most of its time waiting for the HD (I would of thought), and therefore how the OS-HD interaction is managed is important to understand. My OS is Windows 10.

Note. I am not talking about the main thread.

Main vs non-main thread makes zero difference to the speed of reading a disk.

I would have thought that using more than one "other" thread to do the loading to be pointless because the HD cannot do 2 things at once, and therefore would surely only cause disk contention.

Indeed. Not only are the attempted parallel reads forced to wait for each other (and thus not actually be parallel), but they will also make access pattern of the disk random as opposed to sequential, which is much much slower due to disk head seek time.

Of course, if you were to deal with multiple hard disks, then one thread dedicated for each drive would probably be optimal.

Now, if you were using a solid state drive instead of a hard drive, the situation isn't quite so clear cut. Multiple threads may be faster, slower, or comparable. There are probably many factors involved such as firmware, file system, operating system, speed of the drive relative to some other bottle neck, etc.

In either case, RAID might invalidate assumptions made here.