Today I had about a thirty minute power outage while I was out of the house. I got email notifications from my unRAID servers when they switched over to battery and also when the runtime ran out and they were shutting down. Is there a setting to power the unRAID servers back on when the power returns, or is this a BIOS setting and if so, does it work on concert with the unRAID UPS settings?

First thing to check is whether your BIOS power settings has options to restart the computer when power comes on.  If so, is there one which does what you want it to do?

 

Second thing (as I recall), the UPS has to have a setting option in its setup to shut down the output voltage until the input AC power is restored to the unit.  (Most expensive units have this feature, a cheap one may not.)

 

Third thing, you have to consider is where the runtime (and thus battery reserve) is set to start the shutdown.  Remember if the power comes back on ten seconds after you have successfully shutdown the server, you have to have enough battery reserve to conduct another complete shutdown sequence in case the power goes out again twenty seconds after that.  (Just remember that 'estimated' battery run time is a guesstimate and getting last few few percent of run-time is like trying to use that last quart of gas out your car tank while driving uphill!)

I strongly recommend you do not do this, for one main reason. When you use your battery backup for let's say, 15 minutes, it's going to take WAY longer to recharge the batteries than it took to discharge them. UPS's vary, but I wouldn't want to go back on the battery for at least several hours, maybe even a day.

 

If the power happens to go back out shortly after it's been restored, you stand a good chance of running out of battery before the server has time to shut down cleanly.

 

Much better to wait until you can verify the power has been cleanly on for a period of time before you restart the server.

 

If you decide it's safe to do it in your situation, there are a couple things that have to happen. First, the BIOS on the computer needs to be set to restore on power loss, or ac power recovery on, or something similar. Then, you need to be able to tell the UPS to shut off the A/C output after shutdown. APC branded units should work, Cyberpower units may not.

 

Frank1940 ninja'd me as I was replying, but I'll add this to my echo of his statement.

 

Whatever you decide to do, make sure you test that it will work without intervention. It's bad to get it all set up like you think it should be, and find out when the power goes out and you're not around that it ends up crashing your server.

I'll toss in another nickel's worth ...

 

First, your UPS must support powering off after a shutdown, as already noted.  Specifically, if you look at the UPS Settings in v6, there's an option to "Turn off UPS after shutdown."    This is what you want to do.

 

Second, as also already noted, you should not let the UPS run on battery until it's nearly discharged.  Set it to shut down after 5 or 10 minutes of outage ... and leave it like that.    Note you can easily test whether or not it shuts down after an outage correctly by simply unplugging the UPS and waiting for the system to turn off -- then wait a minute or so to confirm the UPS shuts off as well.    Note that the UPS won't shut off immediately after the PC shuts down -- there's no way to communicate an "I'm done shutting down" message, so if you set the "Turn off UPS" option, it's simply told to turn off after a certain length of time, which is longer than the PC needs to shut down.

 

Third, you need to look in your system's BIOS at the power options, and set it to "Always On"  This will cause the PC to automatically boot whenever power is applied to it after a power outage.

 

There is, however, one situation where the PC can shut down and not turn back on.  On SOME UPS units, if they receive a command to turn off in a couple minutes, but power is restored before that timer elapses, they will NOT turn off.    So if you have an outage that results in the server being shut down, but before the UPS turns itself off power is restored; the UPS MAY not shut down.  What SHOULD happen is the UPS should turn itself off; then immediately turn itself back on -- which will result in the PC rebooting properly.  But if your UPS unit doesn't do this, then if that one very specific set of timing happens, your system will remain off.      This is also easy to test:  Unplug the UPS; wait for the PC to shut down; and as soon as it's completely shut down, plug the UPS back in (before the UPS has turned off).    Then wait a minute or two and see if the UPS completes its shutdown and subsequently powers back up.    If not, then you've identified one specific outage sequence that will not result in your server coming back on.