[Nut-upsuser] ordered shutdown

[Arjen de Korte]

Citeren Marco Chiappero <marco op absence.it>:

> I think I know what he meant, because my needs are similar. I already
> explained them some time ago, when I discovered that NUT comes with no
> features at all about programmable outlets (right now I still have no
> shutdown sequence settled yet).
> When you have one ups and many computers with different needs the "low
> battery" signal starts having no use (well, it can be useful but just
> for the last computers you want to shut down).

If you want to conserve power on your UPS, you should simply send a  
client a command to shutdown. While it is shutting down, it makes no  
point to cut the power and after that, the remaining power it draws is  
so small, that cutting power is moot.

You *will* need programmable outlets if you need to restart/reboot  
part of loads attached to a UPS. That comes in handy if you want to  
shutdown some servers earlier than others, to prevent that your only  
option is to power cycle *all* loads to make them start again if the  
power returns before the battery is empty.

We're currently working on implementing this and already have made  
some progress in that direction (see the latest nut-2.4.0 release  
where a repeater mode was added) so you can have 'virtual' UPS  
devices. Basically what is lacking right now, is tying these virtual  
devices to UPS outlets and a way to configure the shutdown/restart  
levels for these outlets. We have some ideas on how to do that, but it  
is currently lacking development time to implement this.

[...]

> In my opinion that's a limitation and, again in my humble opinion, poor
> design. It sounds like refuelling a car on a $TIME schedule rather than
> an avaiability basis: I use to refuel when the *real* remaining fuel is
> below a certain value/charge, do you use to refuel on a *supposed* fuel
> consumption over $TIME?

This is actually how battery charge calculation works on a UPS,  
strange as it may seem. Most (if not all) batteries don't come with  
fuel gauges like your car, so all but the cheapest UPS systems will  
constantly keep track on how much charge is going in an out of the  
battery to calculate the charge in the battery.

Having said that, you should *always* take into account that the  
battery capacity may be less than expected (calculated) due to aging  
batteries, so you can never fully rely on the reported battery.charge  
and battery.runtime. If you search the archives, you'll find plenty of  
examples where people found this out the hard way. This is one reason  
why one should periodically run battery tests to find hidden battery  
problems that only surface under load.

Best regards, Arjen
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