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One Server, Two PSU and two UPS

This is a discussion on One Server, Two PSU and two UPS within the RAM and Power Supply Support forums, part of the Tech Support Forum category. Hi all, We have a slight issue where by in recent weeks our power into the building hasnít been very


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Old 03-14-2017, 08:38 AM   #1
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Hi all,

We have a slight issue where by in recent weeks our power into the building hasnít been very stable causing lights to flicker and the servers to reboot even though they are on a UPS, with surge protection, but not the desktop machines.

We have until today had one single PSU and one UPS plugged into this machine. The UPS is a 750w and the PSU on the server is 1100w!

I have this morning put a second PSU into our main server and plugged this into a secondary UPS, an 800w UPS.

The building only has one mains feed so plugging this into a secondary ring main isnít feasible.

Would anyone recommend this practice, having one server on two UPSís?

I am planning to purchase a 1200w UPS soon though.
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Old 03-14-2017, 08:46 AM   #2
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Quote:
Originally Posted by Dave Cummings View Post
PSU on the server is 1100w!

I have this morning put a second PSU into our main server and plugged this into a secondary UPS, an 800w UPS.

Would anyone recommend this practice, having one server on two UPSís?

I am planning to purchase a 1200w UPS soon though.


I haven't, but I'd be looking at a 1500W UPS at a minimum.
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Old 03-14-2017, 08:56 AM   #3
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phew 1500w yikes. I doubt the power draw is actually anywhere near the 1100 watts stated. Its only got a single CPU and 32gb memory in it
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Old 03-15-2017, 02:36 AM   #4
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Absolutely Mr Cummings. It is pretty standard practice to have you servers/kit spanning UPS' in this manner.
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Old 03-15-2017, 03:53 AM   #5
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Its just Dave (could never figure out how to change my name on here)

Good, so I just need to purchase a new UPS then as it really does look like this one is starting to fail on me!
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Old 03-15-2017, 08:27 AM   #6
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Quote:
and the servers to reboot even though they are on a UPS
If the UPS used to hold the servers during power outages and now don't, that typically indicates it is time to replace the batteries. They typically last for 3 - 4 years. On our mission critical systems, we scheduled battery replacement for every 3 years.

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Would anyone recommend this practice, having one server on two UPSís?
It depends on the setup. Many UPS are designed to be strapped together. But they are from the same maker and purchased as compatible mates. I would not mix and match UPS on the same server as you could end up with the AVR of one interfering with the AVR of the other. You also have to be careful about there not being a common ground which could cause more issues.

If your current UPSs used to support your current servers fine and now don't, there a problem that needs to be addressed. Simply throwing in another UPS is not addressing the problem.
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Old 03-15-2017, 08:42 AM   #7
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the batteries have recently (last 8 months) been replaced. We had a major power outage in December caused by a faulty power strip which basically blew up. I am wondering if the UPS managed to take a hit from that event somehow (even though it wasnt in the same plug socket but on the main ring main) as that is when the problem really started.
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Old 03-15-2017, 09:55 AM   #8
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Quote:
We had a major power outage in December caused by a faulty power strip which basically blew up.
Oh? Was that just a power strip or a surge and spike protector? For the record, EVERY UPS I have ever worked with says you should not plug the UPS into a surge and spike protector (S&SP), nor should you plug a S&SP into the UPS. Because the output waveform of a S&SP is often "clamped" (squared off), the UPS may see its input as flakey, cutting over to battery often and/or stressing (putting too much wear and tear on) the AVR too much. And when the S&SP is on the output side of the UPS, the UPS may see the load as flakey.

Power strips (or S&SPs) don't normally blow up - unless there was some physical damage due to abuse, or you took a very serious lightning hit. And if Mother Nature is out to get you, nothing can stop a determined lightning bolt.

Many UPS have monitoring software that works via an interconnecting cable. If so, most can tell you the status of the UPS, even put it through self-tests. At a convenient time (when your clients don't need server access) I would run that self-test, if you can.

Then there's the conclusive test of unplugging the UPS from the wall and see if the connected computers come crashing down or not. Conclusive, but not very good on computers - or hard drives (and often data) anyway.

I have a table lamp with two bulb sockets that have a 150W incandescent bulb in each that I use to really test my UPS. That 300W load ensure the UPS is capable of supporting my computers.

BUT - a good UPS must be able to detect an anomaly and if necessary correct (regulate) or cut-over to battery backup well before the output of the computer's PSU dies. This may be where you are having problems if your batteries are good.

The ATX Form Factor standard requires all ATX Form Factor power supplies to maintain output during a drop in line voltage for up to 17ms. That's not very long. In fact, if that 17ms were a flicker in the lights, humans could not detect it. And sadly, some of the best power supplies have failed that test and were able to "hold up" power for only 10 - 11ms. :(

Now a good UPS can detect and react to an anomaly in about 5ms - IF it is working properly. And of course, my 300W lamp test does not test for that. It takes some pretty sophisticated equipment to test for hold-up times.

If your UPS took a hit, I would replace them completely, rather than add another. Then relegate those UPS to something less critical than servers. I have my 25 year old APC Smart UPS on my garage door opener! ;) And an old 500VA UPS on my electric blanket!
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Old 03-15-2017, 11:22 PM   #9
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Bill Bright Please explain this
Quote:
You also have to be careful about there not being a common ground which could cause more issues.
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Old 03-16-2017, 03:24 AM   #10
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hi the Power lead was in another room away from the UPS, the UPS doesnt have any spike proection between it and the wall sockets.
I think what Bill is saying if the two UPS's are plugged into the same ring main - eg same electrical circuit (two different plug sockets next to each other) then the "grounding" they will have will be the same ground point, whereas if you had two ring mains and one UPS plugged into each they would have sperate ground points.

I can uplug the UPS from the wall and it will happily power my local computer and its two monitors without an issue, i think this is more and more replated to the load its being asked to carry.
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Old 03-16-2017, 03:36 AM   #11
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Hi Dave, typically the VA rating will give you some indication of what sort load the UPS can support but so certainly ensuring you have the correct capacity is important.

However typically computer kit does not operate at maximum capacity (ie if your server or PSU says 1000w this is a maximum value it can supply under full load) and I would not expect it to do so under normal circumstances. At any rate, any UPS will trip if overloaded so damage to your kit should not occur. This does give you some leeway when making your connections. Some will tell you the load on the them so you know just how much current you are using, but without knowing beforehand at bit of educated guessing can be involved if you don't have more sophisticated measuring methods.

I will simply reiterate. The normal standard method for connecting is Rack/equipment A -B with dual power supplies both have one leg connected to UPS A and B.
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Old 03-16-2017, 07:53 AM   #12
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All connected devices should be connected to the same ground to ensure there is no "difference of potential" between the grounds.

This can some times happen when you have, for example, your computer powered through one wall outlet and the speakers powered through a different outlet on a different wall. This difference might be due to a bad socket or the ground wire in one socket being loose or even missing, or just because the ground wire back to "Earth" ground is longer (thus has more resistance) than the other outlet.

A typical result (if any) might be a slight buzz coming from the speakers. Or in some cases, you might even feel a slight tingle if you touch metal on the speaker and metal on the computer.

This is why in professional studios, data centers, air traffic control and medical monitoring facilities, all the equipment racks are "strapped" together to a "common" ground using a large, often 6 gauge solid copper ground wire that is bonded to earth ground.

Because UPSs (at least the better ones) tend to have very sensitive voltage monitoring and regulating circuitry, if there is a difference in potential between two connected UPS, this extraneous voltage may be seen as an anomaly, causing the AVR to react in some way, perhaps unfavorably.

At the very least, I recommend every computer user have access to a AC Outlet Tester to ensure your outlet is properly wired and grounded. For "mission critical" facilities, having the facility wiring professionally checked is a good idea - especially in older buildings.

Quote:
Originally Posted by Dave Cummings
I can uplug the UPS from the wall and it will happily power my local computer and its two monitors without an issue
Yeah, I have 1500VA UPS and it supports my heafty i7 computer, my network modem, wireless router, 4-port Ethernet switch, home phone, and 2 24" monitors with no problems - easily providing 30 minutes of run time. If I kill one monitor, I can get an extra 15 minutes. And if I kill the other monitor and put the computer asleep, the UPS will keep my wireless network alive for several hours.

Typically servers are "unattended" and don't need monitors running full time. So even the though servers may stay busy, the power hungry graphics solution can remain idle. Even with many hard drives spinning, most power outages last seconds to a few minutes at most and you should not need a monster UPS. If you regularly have extended power outages, you may need to look at a facility UPS, one that runs on diesel fuel or natural/LP gas.
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Old 03-16-2017, 08:47 AM   #13
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the power outages we have had in my year or so here have been less than a second, more "blips" in power (that we know of - when power has been unstable whilst we are in the office) these always appear to send this UPS bonkers!
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Old 03-16-2017, 09:39 AM   #14
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There are times when all of a sudden, all my UPS kick in with all sorts of alarms and beeps, and just as quickly flip back to grid power. I am quite certain these events would result in my computers rebooting. In fact, I believe these type events are the cause of many users experiencing "unexplained" reboots.

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Hmmm, I wonder if I ever spotted you off the end of the RAF Mildenhall runway when I was stationed there from 82 to 86?
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Old 03-16-2017, 09:45 AM   #15
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doubt it I would have been in the foster home and about 4-8 years old! I mainly spot at Manchester, Liverpool, and more recently Hawarden(as my office is right at the end og the runway ish) (I live right in between LPL and MAN) and I run a dreamliner website site - Boeing 787 Register - Welcome
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Old 03-16-2017, 10:11 AM   #16
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Ah I see. And by your site, your self description as a plane spotter "geek" seems quite appropriate. I have spent a lot of time in many countries and plane spotting was definitely taken to the extreme in the UK. RAF Mildenhall was particularly popular with plane spotters because (1) there were two SR-71 Blackbirds stationed there at the time, (2) the base was known to the US military as "The Gateway To Europe" for flights of all sorts of aircraft from the US. And (3) the annual Mildenhall Air Fete air show was, at the time, one of the world's largest.
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Old 03-17-2017, 01:59 AM   #17
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All grounding within a site should be at the SAME potential. if it isn't then you have a fault and should call an electrician.
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Old 03-17-2017, 06:44 AM   #18
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Quote:
All grounding within a site should be at the SAME potential.
"Should" is the operative word. And most likely if the building is relatively new AND wired properly in the first place AND has not gone through any remodeling AND the outlets have not been damaged, then all "should" be fine.

How far you want to take that depends on how sensitive/critical your mission is. If we are talking about medical life support equipment, air traffic control communications, critical data center, a 911 call center, then you need to be 100% certain the facility wiring is totally up to or exceeds code requirements.
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