Good idea. I did check the BIOS and that setting was already enabled. So I unplugged the UPS from the wall to simulate and test. Unfortunately, the server didn’t boot automatically after I plugged the UPS back into the wall. And I remembered that in the past, when the power went out due to storms or something, the server did automatically boot on resumption of power.
I think I know what’s going on.
With the server and a couple small networking devices on the UPS, I get about 16-17min of battery power. After a few minutes on battery power only, the UPS sends the commands to ESXI to start shutting down VMs and then eventually shuts down the server completely. That takes about 10min. That means there’s still battery power remaining, and now with the server off, the largest load on the UPS, the remaining battery time increases to like 40min since the total load on the UPS is now much smaller. However, there’s still technically power being served to the server; there’s even a small light on the back of the server that stayed on the whole time.
Plugging the UPS back in the wall didn’t do anything, which I kinda expected. It’s not going to “send” more power to the server to “wake it up.” I think the only way the server would turn back on automatically in this situation is if the power outage was long enough to completely drain the UPS and turn the UPS off completely. So at least 40min. Then there would be absolutely no power being given to the server. Once wall power is back, the UPS itself turns back on, which sends a little bit of power to the server, which the server BIOS recognizes as “Hey, I was actually without any power at all, but I have power now! Boot!” I’ll test that out next weekend.
So for outages less than 40min, the best bet would be doing a remote desktop into a computer on my network, accessing the web GUI for IDRAC, the server’s out-of-band-management software, and then powering on the server from there. I tried this out and it worked fine.
Not automatic in all cases, but as long as I have a manual means to restart the server remotely, that’ll do.
Sorry for the long post; I wrote this down mostly for myself to work it all out!