Hey folks,
Apologies for the slow response on this thread. This ended up with me, and the last 2 weeks have been a little bit busy 
So, I’ve discussed this issue with our dev team, and I think this is a side effect of how storage works in Roon. Roon is designed to watch your storage devices in real time, and when you add an album it should show up automatically. When your storage device is turned off, the albums it contains should disappear from Roon automatically as well, returning when your storage is turned back on.
There are a lot of reasons the product is designed this way, but one reason is that we wanted to avoid the experience we’ve all had in iTunes where you go to play a seemingly-available song, only to find the media is no longer available.
In practice, Roon will only perform as well as storage devices it’s being used with. As has been discussed quite a bit, many NAS devices do not consistently report changes back to us, and some operating systems (Linux especially, but also macOS) are particularly susceptible to this when using SMB.
Because we need to detect whether the storage device is still on and available, we do check on a regular basis that the NAS is still on and available, and we suspect that’s what is keeping the NAS awake here.
So, the shorter answer here is that Roon is in regular communication with the NAS, and that’s really how our storage infrastructure is designed to work. If that’s keeping the NAS from going to sleep, the only real answer would be for us to change the design, or to use local storage instead of a NAS.
That said, we are going to do some more investigation here. If we are still communicating with the NAS even after the folder is disabled in Roon, that would be a bug. And everyone should feel free to open a feature request related to us changing how storage works in Roon – this would be a big change, so we would want to see real interest in this kind of use case.
If power consumption is the primary concern here, you might consider using a simple USB drive for media storage, and back it up to a NAS that’s only on for a few hours a week.
Hopefully that helps explain the current status of this issue folks – if you have any questions let me know, otherwise we will schedule some testing in our QA department once the dust from 1.5 settles, and we will let you all know if we’re able to identify anything that’s not working as designed. Thank you!