Here are some resources for anyone interested in learning about I/O completion ports. I first introduced I/O completion ports in a series about parallel programming with asynchronous procedure calls (APCs):
I/O completion ports define a threading model for supporting scalable I/O but it is not very easy to get it right. The hardest part is thread management. Fortunately, the kernel developers responsible for operating system threads later introduced the Windows Thread Pool API. This is a very thin abstraction over I/O completion ports. This is what you should use today instead of relying on the I/O completion port functions directly. I wrote a series about the thread pool for MSDN Magazine:
Naturally, any topic related to I/O and threads requires a good understanding of Windows synchronization. Here are a pair of articles that will get you up to speed:
I also illustrate many of these techniques in my Modern C++ Concurrency course on Pluralsight.
Finally, if Microsoft needs help fixing Windows.Storage then just let me know. 🙂