On 30/09/14 05:28 PM, Valeri Galtsev wrote: > > 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 Some of our clients have that, but not all of them. Even the ones that do, though, can have trouble. A different recent client had a major incident in their power distribution room (fire and/or explosion). They had enough fuel for 6~8 hours of operation. They couldn't get more fuel in time and ended up having to shut down their production facility until they could arrange a more long-term solution. You can go to great lengths to protect yourself, but there will always be limits. It's a question of where your paranoia and budgets meet. -- Digimer Papers and Projects: https://alteeve.ca/w/ What if the cure for cancer is trapped in the mind of a person without access to education?