I've got an old (but trusty) Synology DS215j NAS. Cheap and cheerful. The only down side is that until recently you couldn't keep it off.
The NAS has been working fine for years. It has an auto start-up/shutdown feature which I use to turn it off overnight when it’s not doing backup or media streaming duties.
Recently though it seems to sporadically turn back on. After noticing this and ignoring, I finally sat down recently to troubleshoot and try and fix. I adjusted the auto on/off to turn off at 1pm, then back on 15 minutes later. It turned back on almost straight away. I tried some other time variations, it always came back online quicker than planned, often just seconds later.
The Usual Suspects
I tried a software update. No change. I also tried disabling the auto power on/off and just doing a normal shutdown, it just turns back on seconds later as well!
Queue some deep Googling… It was proving to be a hard problem to search around as lots of the suggested results covered servers that are stuck on or off, but very little about turning off and staying off.
Bad Batteries
Eventually, buried in the search results, was a suggestion about changing the CMOS battery. I don’t think I’ve changed a CMOS battery in a computer for years, it didn’t even occur to me that could be the cause, although in retrospect it makes sense, something has to keep track of either power failure (so auto-on after power failure works) or the time (for auto on/off scheduling).
Sure enough, with a new CR2032 battery inside the unit a little later, the immediate power on problem was fixed. Re-enabling the auto power off/on also now worked fine.
The solution was easy to execute but hard to find. Afterwards I felt almost duty bound to write this short blog post about it, to hopefully give a little more signal out of the noise online for anyone facing similar issues. If your Synology NAS is showing unexpected behaviour with powering on when you expect it to be off, change the CMOS battery.