On Tue, September 30, 2014 2:13 pm, Digimer wrote: > On 30/09/14 03:07 PM, Valeri Galtsev wrote: >> >> On Tue, September 30, 2014 1:41 pm, Digimer wrote: >>> On 30/09/14 02:33 PM, John R Pierce wrote: >>>> so I have a bunch of servers at work that are on DUAL UPS's (1 per >>>> each >>>> of 2 power supplies). >> >> The only thing that stopped me from doing that was: you can only use >> each >> UPS up to a half of its spec'ed current drain. >> >> Thinking in line of: having 2 UPSes for rack, how do you distribute >> power >> from them to machines which luckily have 2 power supplies each (for >> redundancy). Having 1 PS wired to one UPS and 2nd PS to second UPS will >> save you if one of UPSes failed (and does not provide any output AC). >> But >> in this case you will need UPS as powerful (current drain wise) as to >> power the whole rack. So you are paying for reliability by using UPSes >> of >> double capacity. Did I not miss anything? I guess I almost did: if you >> have 4 UPSes for 2 racks you can wire them so that if only one of 4 >> fails, >> you will have increase in draw of all UPSes only by 1/3... >> >> I decided _we_ are not that rich anyway... > > In our case, that is what we do. We're an HA shop, first and foremost, > so *everything* has to be redundant. So yes, each UPS, on it's own, has > to be able to hold up all equipment for the minimum specified runtime. > That said, it's not really a "waste", because when there is a total > poewr out, we get twice the minimum hold-up time, which comes in very > handy at times. > > For example, we had a client who runs Windows VMs on out system. There > was a major power out event that we knew was going to outlast the backup > power (they're a manufacturing facility, so if the machinery isn't up, > then the servers aren't doing much). After we determined that we had to > shut everything down, we found that someone had not turned of MS's > automatic updates. So one server decided that it was a great time to > install updates during a critical outage. > > Thanks to having the extended runtime, we were able to shed some load > and hold up the host node and the server long enough for windows to > finish all of it's OS updates. Obviously, this should never have > happened in the first place, but it's an example of how extra runtime > can come in super helpful. > Which asks for one more piece of equipment (hopefully you are not on a high floor...): diesel generator. That kicks in if the power doesn't return after some short outage. (I was almost sure you mention it somewhere closer to the end...) Valeri ++++++++++++++++++++++++++++++++++++++++ Valeri Galtsev Sr System Administrator Department of Astronomy and Astrophysics Kavli Institute for Cosmological Physics University of Chicago Phone: 773-702-4247 ++++++++++++++++++++++++++++++++++++++++