[Nut-upsuser] UPS Groups?

[Charles Lepple]

On Oct 15, 2014, at 2:50 PM, Michael Stinaff <mstinaff at gmail.com> wrote:

> My thinking was that this provides the following benefits:
> 1. When anyone needs to interface with the UPS Master there is no ambiguity. There is only one.

(See below)

> 2. All servers are slaves so any server can be dropped, rebooted or nuked without affecting any other server.

Agreed, although if you set things up for "MINSUPPLIES 1" and have one NUT upsd per UPS, e.g. UPS A1 with Server A1, and UPS A2 with Server A2, you can still take down one of A1 and A2 under good power conditions, and the rest of the servers will not shut down unless *both* A1 and A2 disappear or lose power.

> 3. (What I am not sure NUT can do) Each slave monitors either UPS group A or B depending on what it drawing power from.  If that group drops below MINSUPPLIES then those slaves shut down.

It is easy to do set up the configuration files manually. Working from your diagram, the Central NUT Host exposes four UPSes: A1, A2, B1 and B2.

Server A1 lists A1 at central and A2 at central in its upsmon.conf, and Server B1 lists B1 at central and B2 at central.

What makes this potentially difficult is whether or not each UPS has a unique serial number exposed in its USB descriptors. If not, then you will run into problems telling the second, third and fourth drivers which UPS to talk to. USB bus numbers in Linux are not guaranteed stable across reboots, or especially kernel upgrades. That would make the Raspberry Pi solution a little more attractive. (Built-in serial ports do not typically suffer from this shifting name problem, but add-on PCI cards might.)

One thing we will be rolling out soon is a library of upsc "dump files" that show a representative set of data from various UPS models. It's still on our CI server now, but this link should be good:

http://buildbot.networkupstools.org/~buildbot/cayman/docs/latest/ddl/

Or check out the raw Git repository to grep for 'ups.serial':

https://github.com/networkupstools/nut-ddl

APC often includes serial numbers, as does MGE. Tripp Lite tends to include it on higher-end models, but beware of the serial numbers that start with "FW" and seem short - they look like they are firmware versions.

> That said the Central NUT Host would need to be able to survive any combination of UPS outages.

If it has enough redundant supplies, it should not be a problem. But then it becomes a single point of failure in terms of software and networking (bear in mind that the network gear between the central server and the slaves needs to be powered from an UPS as well).

> Maybe instead I put a Raspberry Pi with one of these
> http://www.seeedstudio.com/depot/lipo-rider-pro-p-992.html
> on each UPS pair.  Any thoughts on that solution? 

I would be interested to hear testing results with that hardware. I have been trying to do something similar with a NiMH power supply and a Raspberry Pi Model B, but it does not seem reliable under load:

http://www.ghz.cc/charles/NUT/OpenElectrons_SmartUPS.html

On the other hand, in my application, I am more concerned about shutting down the Pi cleanly, rather than keeping the network connections up.

-- 
Charles Lepple
clepple at gmail