I don't really use W8 anymore; I assessed it for 6 months, tried to like it, tried to fix the broken UI with 3rd-party addons/apps, then reimaged back to W7 and it was like a breath of fresh air. I missed nothing from W8 when I switched back :\
As such, I can't really help you with your w8 ntoskrnl issue - but the obvious Microsoft "murder your disk with IO" processes have historically been dynamic swapfile resizing, indexing, and superfetch. Try fixing/disabling each of these in turn and seeing if it helps your disk behave.
Unfortunately, Sysinternals Diskmon got gobbled up by Microsoft and I don't think the older versions work on 8 - though you could always try it.
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