[Nut-upsuser] ordered shutdown

[Arjen de Korte]

Citeren Marco Chiappero <marco op absence.it>:

> Well, right, but PSP it's not intended for network use, while NUT indeed
> it is. I took it as example for showing the above reason and how easy is
> to choose from different criteria in a standalone environment:
> http://i39.tinypic.com/2mpy9s6.png

You hit the nail on the head. While it is fairly easy to change  
shutdown parameters in a standalone application, this is not so easy  
in a networked environment. In a standalone application, you can rest  
assured that once the shutdown condition has been reached, the system  
*will* go down and recovering from that is fairly straightforward too  
(since this will be dealt with by the UPS itself). No need to deal  
with transient conditions.

In a networked environment with multiple shutdown levels, you'll also  
have to deal with transient conditions and also with the situation  
where the power returns between two levels (and how to recover from  
that) and making this system fail safe too. This is vastly more  
difficult to handle.

> If I'm not wrong it should be pretty easy to set up ordered shutdown
> with different criteria in apcupsd too. Me and some other people
> reported that actually NUT can't easily cope with similar requests. Is
> there something more to comment on that?

Yes, there is. If extending runtime by shutting down loads is  
essential to you, chances are that what you really need is a generator.

Most of the power outages you'll experience in everyday life will be  
short lived (in the order of seconds, mainly due to switching  
operation in the grid), which are corrected automatically. This is  
something that can dealt with easily with the runtime of basically any  
UPS in existance.

Longer outages are usually mean that something is broken that can't be  
corrected automatically and/or requiring human  
intervention/replacement of systems. This means that the outage will  
be much longer than the runtime of UPS batteries. No matter how much  
load you're shedding. Even at no load, most UPS systems won't hold up  
longer than about 45 to 60 minutes. If you've already used up part of  
the juice, it will be even less. So you're systems *are* going down in  
that situation.

If losing (some) systems is really a big deal to you, having a UPS is  
only part of the solution. Personally, I feel the option to shutdown  
part of the loads depending on battery charge or runtime remaining is  
largely a waste of effort. You'll still have to deal with the  
situation where the battery state triggers shutdown on all systems at  
the same time (after recovering from an outage, followed by another  
outage for instance).

[...]

> So, I'll keep waiting for the features. :-)

...instead of working toward a solution. You see where the root of  
this problem lies? The active developers don't have this high on their  
list of features and the people that want this, don't provide any help  
in adding them.

Don't hold your breath waiting. ;-)

Best regards, Arjen
-- 
Please keep list traffic on the list