How can I monitor whether my HDDs are in standby?

How can I monitor if/when and for how long my hard drives go into standby?

I've a Windows Server with a RAID5 (software) for data and another regular disk on which the OS is installed. I want to make sure that the RAID goes into standby when no data is read (i.e. no background task I'm currently unaware of accesses the drives and disrupts their standby).

Ideally, I'd like to see some sort of graph that has the last couple of hours on the x-axis and the disk state (busy, idle, standby) on the y-axis.

Is there a tool that does that or do I need to code it myself? If so, can I access this information via a command line tool or do I need to dig into the depths of the Windows API?

Edit: It would of course be completely awesome if such a tool could log which process interrupted the standby.

If you're looking to just be able to look at a window and see if the disks are being accessed, the Resource Monitor (accessible through the task manager) will let you look at what processes are reading/writing what files (and from there you can see what partition the files are on). If you want it logged, I believe this should be doable through creating a log in the Reliability and Performance Monitor, though apart from pointing you in that direction I can't give a step by step process.