I do recall sar...  Definitely one of the classic tools for analyzing disk activity.  It's probably worth some learning curve to attempt it.

I have never gotten terribly deep with any of these tools.

If there's something modern and either

A) brainless easy, or

B) deeply better

That would be awesome to know of.

sar and iostat are the ones I always remember.

I seem to recall sar being a bit risky to use as it might induce a fair bit of I/O load itself.