Rack power and power available

[PCER]

Good morning.

 

Can anyone confirm some power requirements? Working backwards from a 42U rack, what would it need to contain to be full, and what power would it use? A rack seems to need a 16 amp supply but my power supply is in Watts and at 240 volts. Thx.

[mjs_mjs]

What devices will be in the rack? as a rough guide 13a is 3.12KW, 16a is 3.84KW. hope that helps?

[jamesreedersmith]

Too many variables here - are you loading it with UPS's, Servers, Switches or just patch panels

How many servers and types, models, loaded specification, load on the server, single or dual psu;s

How many switches are the poe or not - if they are poe are all ports fully loaded with haevy weight devices or just ap's.

How many UPS = are the ups only powering the rack or is there standard servers at the side too.

Any NTU's powered KVM's, monitors?

[Butuz]

If your loading a 42u rack full of new servers you'll be needing a 32 amp supply. Half full you could just about get away with 16 amp depending on the servers.

 

Your question is a bit confusing. Watts = Amps x Volts. So amps = Watts / Volts. You should be able to work out your amps.

 

Butuz

[Fuzzz]

Watts = Amps x Volts. So amps = Watts / Volts. You should be able to work out your amps.

Butuz

 

That's only true if you have Power Factor Corrected (PFC) PSU's (which most servers have). However, most UPS'es are not PFC and will supply about 60% of the V/A-rating in Watts (ie a 1000VA UPS will support about 600 Watts).

[PCER]

Thank you for replying, I have thanked each of you.

 

The 42U rack would have in it as much as the 240V supply could handle! So that would be servers, a PDU, and whatever else would be needed, a 1U keyboard, any cooling? Someone says he has a 315V supply so the rack could be powered there if that's right.

 

If there was 32 amps for the 42U rack, does it follow that 64 amps would be required if there was then another rack added to the same supply later?

[mjs_mjs]

it's pointless talking about supplies until you know what exactly is going into them....

[Domino]

yeah, you don't power the rack - you power the contents....

 

So spec a UPS for the servers going into it, with PDUs as needed. the Rack is just a storage unit (unless its got fan modules in)

[PCER]

Yes. What to put in? The Dell R900 is 4U and takes up to approx. 1500W. A PDU is 2U and powers 3 servers up to 60A. A 42U rack could hold 8 R900s, 3 2u PDUs, and a KVM, leaving 3U. I assume the UPS is situated elsewhere and covers the entire power supply. At 230V single phase, each PDU needs to deliver 55A for the R900s at full power, which is right with the PDUs at up to 60A.

 

Cheers for reading.

[mjs_mjs]

upto being the key word.... putting 63A into a rack is allot of power and i would be concerned with that. do you have access to a power meter? as yes they may be rated upto but realistically it's probably less. Also 8*1500 is 12KW which basically will be heat, how much cooling do you have available for that?

 

i personally would be more inclined to get out a meter or buy a cheep one and look at how much power is ACTUALLY being used. i asume you have redundant power supplies so you should be able to do that without any downtime.

[Andrew_C]

Sorry to say this, but you seem to be so far from understanding really basic electrical theory that you need to get a professional in to design the system for you. I don't know of anywhere in the world that has a 315v supply.

 

We cannot give you an answer to your question, when you don't really know what the question is!

[PCER]

Hello and thanks. Yes, thats 415V of course, 3 phase.

 

If a 42U rack cannot actually hold all the equipment, why are such tall racks available? Assuming that there is cooling in the computer room and/or warm aisle or cold aisle cooling, how much could actually be put in to the 42U rack? The 1,500 W is at full load anyway so the calculation allows for max power which there probably would not be. The servers using 1,500W are for virtualisation and have 256GB SDRAM which could allow for quite a few users if each has a guaranteed part of the SDRAM of less than 1,000MB each.

 

A main thing is that one rack takes up the space of one rack so why leave part empty and then get a second rack taking up more space and yet again leave it part empty?

[Domino]

The rack is just storage, you can fill it with whatever you like.

 

servers, switches, patch panels, whatever.

 

The rack doesn't care how much power is being supplied to the kit thats in it - its a metal cage.

 

There's guidelines for how much should be supplied to a single cabinet, but really you want to work the other way round - how much kit do you need, then how much power does that need, then how do you supply that power (UPS and all)

 

theres a hp tool that lets you simulate power load based on the kit you'll be using - do dell do something similar?

[dhicks]

However, most UPS'es are not PFC and will supply about 60% of the V/A-rating in Watts (ie a 1000VA UPS will support about 600 Watts).

 

Thanks, I was wondering about that - was a tad puzzled why the UPS' (UPSes? UPSi?) I installed over the summer didn't seem to match up VAs and Watts. Now I've moved schools I might have to do the whole thing over again with a new set of servers - the power requirements are something I'm going to need to bear in mind. Also, it's worth pointing out that a fully-loaded 42U rack is going to weigh a fair bit and you need to check that your floor can handle it. Anyone who doesn't belive me can come along at half term and give us a hand hauling the server rack out of the floor...

 

--

David Hicks

[john]

Also, it's worth pointing out that a fully-loaded 42U rack is going to weigh a fair bit and you need to check that your floor can handle it. Anyone who doesn't belive me can come along at half term and give us a hand hauling the server rack out of the floor...

I take it you've had a floor issue and your rack has sunk slightly?

[dhicks]

I take it you've had a floor issue and your rack has sunk slightly?

 

Indeed. Actually, the air conditioning condensate outlet came adrift sometime over the summer, leaking water on the floor and turning it soft and moldy, at which point a corner of the rack went through the floor, into the ceiling of the photocopier room below. No real damage, but we have an embarrasingly lopsided looking rack at the moment.

 

--

David Hicks

[Domino]

Pics or it didn't happen ;-)

[john]

Pics or it didn't happen ;-)

 

Must agree, I think some pics are required on this

[dhicks]

Must agree, I think some pics are required on this

 

Might be tricky - there's so much stuff wedged in to the server cupboard I can hardly get in. I did manage to figure out what the old server on the floor is used for, though - it turns out it's propping up the rest of the rack.

 

--

David Hicks

[Chillibear]

Yes. What to put in? The Dell R900 is 4U and takes up to approx. 1500W. A PDU is 2U and powers 3 servers up to 60A. A 42U rack could hold 8 R900s, 3 2u PDUs, and a KVM, leaving 3U.

 

8 R900s is quite a serious amount of kit, if you can afford to buy the best part of £60k (list) of servers I'd be tempted to pay for some assistance in sorting our your electrical supply. Given electricity costs in data centres I really would speak to whoever will be hosting this lot to discuss the best way of handling it in their facility.

 

If a 42U rack cannot actually hold all the equipment, why are such tall racks available?

 

Because even a 1U rack would take up the same amount of floor space! It all depends on what you put in your racks, some kit is bulky, but doesn't draw huge amounts of power - if your network patching is rack mounted (as opposed to frame mounted) then you can loose a lot of a rack just down to patch panels. I've always ended up filling racks without a problem! You always find something to put in them.

 

Assuming that there is cooling in the computer room and/or warm aisle or cold aisle cooling, how much could actually be put in to the 42U rack?

 

Speak to whoever owns/manages the computer room. Is this a facility you manage or are you colocating your equipment with someone else? Assuming the facility has already been built then chances are the power supplied to each rack will already have been determined. Making assumptions about the cooling is always a big mistake, ultimately no matter what the power feeds to a facility are it will be the cooling capacity that determines the amount of kit that it's sensible to locate in the facility.

 

The 1,500 W is at full load anyway so the calculation allows for max power which there probably would not be. The servers using 1,500W are for virtualisation and have 256GB SDRAM which could allow for quite a few users if each has a guaranteed part of the SDRAM of less than 1,000MB each.

 

The only real world figures I've seen for the R900 was a draw of 800W under load, which would seem about right, although that will vary depending on configuration.