UPS for more than one server

Gordon Henderson gordon at
Thu Nov 2 02:15:17 CST 2006

On Tue, 31 Oct 2006, Alessandro FAGLIA wrote:

> Dear list,
> I am going to buy two PE850 server, and I would like to have only one
> UPS. Boxes will run last Debian stable.
> The first machine is a RAID1 on two 160GB SATA disks with CERC card,
> while the second will be a RAID5 on three 160GB SCSI disks with PERC
> card.
> The online self-making server procedure suggests two UPS models:
>  *  APC Smart-UPS 1500i, 950Watt, rack mount (2U)
>  *  APC Smart-UPS 2200i,1600Watt, rack mount (2U)
> >From PE850 technical specifications, I read that the system needs 345W.
> Do you think the first UPS model will be enough for two machines?

Theres a general rule I'd found to work with most UPSs over the years - at
half the rated load, you'll get 15 minutes, and at full load you'll get 5
minutes. At 345W you're putting less than half the load on the first one,
so it'll be fine for at least 15 minutes. However it all depends on the
batteries installed - the the 2nd one has the same batteries but just a
beefier power board then this won't hold true! But you're inside the
limits and less than half the load, so that ought to be "just fine".

One other thing to note is that most UPSs quote VA which aren't quite the
same as Watts. There is a power conversion factor and it's to do with the
type of load the equipment is putting on the UPS. Purely resistive loads
like light bulbs and heaters are more or less 1:1 but weird switch-mode
power supplies are less - but it looks like you've got those numbers
anyway - the 1500i will very probably be quoted as 1500VA, but you've
quoted 950W which is about right. (It's marketing crap, just selling
HiFi's based on "Peak Music Power" rather than RMS Watts)

> Moreover, I have the following additional question.
> I would like to manage the automatic shutdown of machines when the UPS is
> running out of battery. Normally I manage this with a service (e.g.
> rupsd) running on the server and communicating over RS232 with the UPS.
> Will I be able to do that with the UPS I am going to buy (e.g. do they
> have the ethernet adapter to do this)?

You'r have to check the specs to see what sort of connections they have.
>From what I remember the smaller rack-mount APC units now only have USB.

> Can anybody give me some hints in order to implement what I'am asking?
> I read something about SNMP traps, but I cannot find something more
> specific on the net.
> I will be grateful if somebody can point me some howtos on the Net.

NUT - Network UPS Tools. Debian has in as a package, but you might want to
look at the latest drivers. One "master" can signal all the others to
shutdown if required.


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