[Nut-upsuser] Networked APC

[Charles Lepple]

On 8/1/06, Charles Lepple <clepple at gmail.com> wrote:
> On 8/1/06, Matthew Isleb <misleb at pnca.edu> wrote:
> > On Aug 1, 2006, at 11:05 AM, Charles Lepple wrote:
> > > You still may end up with a single point of failure, though, since you
> > > probably only want one machine commanding the UPS to power down. (A
> > > data center could avoid this with dual-input power supplies fed from
> > > separate UPSes.) Someone else who is more familiar with snmp-ups may
> > > have more insight into this.
> >
> > Eh? Why would I want to command the *UPS* to power down? The UPS will
> > power down if and when the battery goes dead.
> >
> > Or did I misunderstand that? I want all my servers to power down
> > using the UPS itself as the "master" instead of picking a server as a
> > master.
>
> Right, when the UPS sends a low-battery signal (or has been on battery
> for X minutes, etc.), you can tell it to shut off the load. This can
> be handy if you want to briefly turn something back on during a power
> failure.
>
> It's all a matter of taste, of course... but the default NUT
> multi-machine setup is to have one "master" that talks to the UPS, and
> directs the slaves to shut down. Then, when all the slaves have shut
> down, the master shuts down, and sends a power-off signal to the UPS.
>
> Whether the UPS is smart enough to do it, or if NUT has to command the
> UPS to power-cycle the load, you probably want a contingency plan for
> power-cycling devices if the power returns after machines have already
> shut down. This is the most common race condition that inexpensive
> UPSes fail to take into account, and it will leave you with a bunch of
> halted servers when the power comes back on.

What I said above is true for NUT drivers in general, but apparently
the current versions of snmp-ups only monitor the UPS (and does not
shut it down, although the protocol allows for it).

Arnaud knows much more about the snmp-ups driver than I do, so I will
defer to him.

-- 
- Charles Lepple