But this could be handled smarter.
Unfortunately, what you're hitting is a limitation of Windows. Filesystem Access is UI blocking.
Let the drives sleep and open Windows Explorer (not MC) and browse to the same files on the share, and you'll see it hang in the same way. MC doesn't have a choice. If it tries to access the files in any way, Windows doesn't return control to MC's code until the drive spins up and returns data, or the network attempt to access it times out. The end.
Also, I admit that I skimmed this thread, but... Are you using those drives in JBOD mode? Eg: Not as an array, but just as individual disks? If so, that's a crazy way to try to store 60TB on a NAS. You'd be much, much better off running all the drives in a RAID-6 array (or at least RAID-5, though be wary of those with that many disks). Otherwise, the fact that individual drives are spinning up when accessed doesn't make any sense (the whole array should light up on first access).
And, make sure you don't have a bunch of misplaced or offline database entries in MC which are trying to spin up network volumes that don't exist. For whatever hangs you see with sleeping drives, it is 100x worse for any network drive that doesn't exist anymore (because Windows waits for the 200 second, or whatever it is, timeout). Make a Smartlist or View
that shows files missing from disk, and make sure you don't have any nonsense in the Library.
And, lastly, the answer is simple: don't sleep the drives in the array.
If it is
actually overheating when the drives are spinning but idle, then it'll sure-as-heck overheat when you're actually using the disks! The answer to that isn't to sleep the drives, it is to add better cooling. If it isn't actually overheating, and you're just worried about it, then you may very well be trying to fix an issue that doesn't exist, and suffering for it.
If you're trying to save money on energy, then you really have to do some deep investigation to determine what the cost vs benefit of sleeping the drives is vs just leaving them on. If you use your media most days, it will almost certainly be a difference of cents over months between an aggressive sleeping setup and just spinning them all the time. Spinning the drive up is
most of the power used by a drive. Once it is at speed, keeping it rotating requires a fraction of the power (conservation of momentum). And, evidence for this is somewhat anecdotal, but spinning them up and down all the time
must be harder on the drive bearings and motors than just leaving them spinning all the time. In enterprise array setups, the drive sleeping functions available in RAID systems are almost always used only for cold-storage or semi-cold storage systems. Anything that is going to be accessed a few times a day, you're looking at seriously diminishing returns.
So, if you really want to know, you need to get a power meter that can measure power at the plug on the NAS over time. Hook it up to the system as you have it now, and then use it normally for a couple weeks. Then, change it to always on, and record for another couple of weeks. Then look at the power differences. I'm all for saving the Earth (for sure) but you'll probably be surprised at how little difference there is.
And, instead, replace an incandescent bulb or a couple CFLs with LED bulbs instead and you'll be saving way more power.