Quote Originally Posted by Ao1 View Post
Boy storage is complicated stuff. The more I think I've learnt the more I realise I don't know.

HIOmon is really helping me though and I really appreciate your insights.
I've noticed that the ReadSystemCacheIOPcount and ReadSystemCacheIOPmissCount (same with writes) are always 0. I think the only exception was when I ran the winsat disk benchmark.

What does that tell me?
I certainly agree: storage in general is inherently pretty complex.

The wide range of summary metrics made available by the hIOmon software provides an explicit reflection of this complexity in large measure.

Of course, the complexity involved in actually capturing/collecting/exporting/etc. these summary metrics is yet another matter!

Anyway, regarding the ReadSystemCacheIOPcount and the ReadSystemCacheIOPmissCount metrics, these metrics reflect read I/O operations that, as observed by the hIOmon I/O Monitor, were directed towards a file and which explicitly requested the use of the system file cache. The same applies to the write variants of these metrics as regards write I/O operations.

As such, they only pertain to file-level I/O operations. Accordingly, these metrics are not applicable to I/O operations that are observed by the hIOmon I/O Monitor at either the physical volume or the physical device level within the operating system (and so, of course, their value will be zero in these cases).