IOS – external drive for ios products

Sure this problem applies for both your drives? Could be that one drive affect the other thru your USB controller. Try to disconnect one of them and see it it gets better. If it doesent, swap them to see. If it gets better while one of them is disconnected I would limit the problem to be a faulty drive.

You could also try to check if some processes are accessing your drive. Have you checked torrent or so aren't loading to the drive(s)?

Alternatively you could turn off the option for spinning down your hard drives when possible in your settings panel for power.

Theoretically? Yes.
Practically? No.

You would first need to build nfs for iOS. Then, you would need to make the YouTube downloader application save its movies onto the network drive. As far as I can tell, nobody has worked on nfs for iOS, so unless you know a lot about programming for iphoneos-arm, you might just be out of luck. You wouldn't be able to extend the user partition onto the network drive, though, so none of this would be transparent to the apps. You could symlink the Documents folder for each app that you'd like to have access to your network drive, which would give you the same effect (assuming you can get your drive mounted).