Our current, old, due to be replaced, environment is very bogged down by the disk subsystem, or at least that's the way it seems (Using the free Idera SQL Check we see a high waits, 3600ms/sec on average, and on average 30% CPU utilization). I know that's very over simplified, but I'm not going burden folks with details unless they ask.
We've been given tentative clearance to buy new hardware (sub 10K USD), but how can we validate whatever we recommend will deliver faster I/O?
I realize the answers to my questions go down some deep rabbit holes, but need to start somewhere. Using this article, we downloaded this tool and did some basic testing.
High disk waits don't cause high CPU time. High disk waits are also not a definitive indication that the hardware has a problem... it's a possibility but not a confirmation.
Considering the CPU time, I'd say you need to work on the code before you go buying hardware because it may not actually be a hardware problem.