OT: Looking for some inpiration with UPS setup

Christopher Key cjk32 at cam.ac.uk
Fri Nov 9 08:34:31 PST 2007


Apolgies for the slightly OT post, but I'm hoping that some of the 
ammased expertise might be able to suggest a solution.

I've a FreeBSD fileserver, a solid state router (Linksys box running 
OpenWRT) and a couple of gigabit switches that I'd like to move onto a 
UPS (I'm primarily looking at the APC Smart-UPS line).

The requirements for the FreeBSD system are pretty simple, it's not 
likely to be of any use if the power's out, so after a few minutes to 
allow any files open over the network to be saved, it should perform an 
orderly shutdown and remain off until the power returns.  However, the 
router is a little different.  It maintains some state information in 
RAM (dhcp leases etc) that I'd prefer not to lose during a short power 
outage, and it would also be useful to retain internet access, so 
ideally I'd like the router and switches to stay up for as long as the 
battery lasts in the UPS.

Space and budget are limited, so ideally I'd like to achieve all this 
with a single UPS, which is where the problems arise.  As I understant 
it, when the UPS wants to wake the attached machines up, it power cycles 
its output.  This however will reset the router, which was what I was 
hoping to avoid.

I've thought around the problem for some time, but not come up with any 
convincing solutions:

1) Use some sort of WOL command from the router to the FreeBSD system 
rather than having the UPS power cycle its output.  How does the router 
know the power's returned?  Can the UPS be set not to power cycle its 
power output when the power returns?

2) Use a second cheap UPS to 'protect' the router whilst the primary UPS 
cycles its power output.  This seems rather crude, and would presumably 
reduce the battery life of the primary UPS due the losses in the second UPS.

3) Have the UPS wake the PC via some other means.  USB would seem to 
ideal choice, but the motherboard won't do a wake on USB from S5, and 
I'm can't find a UPS with an ethernet interface.

4) KISS.  Buy two smaller, cheapers UPS units.

Does anyone have any clever ideas for a solution?  Any thoughts much 



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