I have a synology nas and is unable to stop the spinning disks. A shame, every other thing in it is nice, but could have beter optimizations, as the disk are the most of its energy consumption.
You can set the power options so that it can shut down after a period of inactivity. Mine has 8 HDDs. According to my power meter plug, it uses 70W when all are spinning, 30W when the drives are spun down, and about 3W when "off" (configured to WOL). When I need to use the NAS for a while, I usually bring it up via an SSH app on my phone, which connects to my always-on Raspberry Pi that can send the magic packet. I use the wol package in Arch.
I also have a Synology nas, a DS413 for 10 years now.
and I use it like this also for 10 years now. It works great. Only consumes ~4W in deep sleep/system hibernation (the wording depends on from which year you find text mentioning the above nas. Synology decided to reword the function back in some year), and automatically wakes up whenever it is needed.
(also not this is not only HDD sleep, it is full system sleep)
