Re: [57north-discuss] Dell Servers - Calculations etc

2014-04-11 Thread Calum Enterobsidian 
On 11 Apr 2014, at 10:04, Tony Travis tony.tra...@minke-informatics.co.uk 
wrote:
 Hi, Calum.
 
 I've no experience of the Dell systems, but modern PSU's are designed to
 be 80% efficient (i.e. 20% of the electricity consumed by the PSU is
 dissipated as heat). Most servers use PSU's that are ~50% over-capacity
 because of high start-up currents. In addition, typical CPU heat
 spreaders are rated at ~100W per socket maximum. This sets an upper
 limit to power consumption regardless of how many cores are in the
 processor. In practice I observe ~250-350W power consumption (according
 to CPU activity) by each of my two dual 2-core (Opteron 2212) processor
 servers running with 32GiB RAM and 16@500GB disks in each although the
 PSU's are rated at 700W. The 2U Opteron 200 systems I donated to the
 Space draw about 150W each. I think you're right to be concerned, but
 I think that your power calculations are a bit on the pessimistic side.
 
 Bye,
 
  Tony.
 

Hi Tony,

Without knowing what each server actually draws, max load was the only thing I 
had to go on when I did these quickly at 1 in the morning. They assume that the 
server is in its worst possible loading condition, so it's taking the full 
power available from the output - max stall load. 

I think the main constraints we are going to have are the wiring in the 
building and the loading capacity of the floor. Without looking at both I can't 
give an accurate figure accurate figure beyond 8, as the MSL may exceed the 
wiring specification. It loos like the building may the biggest factor in the 
selection.

Regards
Calum
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[57north-discuss] Dell Servers - Calculations etc

2014-04-10 Thread Calum Enterobsidian 
Hi guys,

I've run a few calculations to try and work out how many servers the space can 
use.

The calculations assume that there is a dedicated pair of 13A main sockets for 
the server rack, and that they will conform to specifications and carry the 
current without any problem. 

The 1950 model has the follow specs:
Power supply: 670W
Weight: 16.3kg 
Height: 1u

The 2950:
Power Supply: 750W
Weight: 26.76kg
Height: 2u

Based on these values, I would not recommend using more than 8x 1950 servers 
over the 2 sockets (ie 4 per pdu, with each pdu plugged into a socket). This 
combination will draw 5.36 kW, and even at this there may be little overhead 
for any problems with cables or heating. 

8x 1950 servers will weigh 130Kg (I believe without rails) which is on top of 
the weight of the rack. It is up to the committee to decide if it is suitable 
for this much weight to placed on top of the current weight in that area. 

8x1950 will put out around as much heat as 3x 2kW heaters, so consideration may 
have to be given to providing some form of cooling for the room, especially in 
the summer months. 

The above set up would give 64 cores assuming quad core CPUs in both sockets of 
each server. 

Using the larger 2950 in 12u would result in 6 servers, which is 160.56kg, 
4.5kW and 48 cores. 

These figures use maximum levels for values, actual consumption may be less, 
but if the server is running near 100% then these will not be far off. I would 
not recommend running with the combined power supply values being greater than 
the 2990kW provided by a 13A plug. Some overhead for cable heating, allowance 
for old cabling, etc should be left as well.

I may be around tomorrow, in which case I will try to sort something out with 
getting these into the space, but there is no guarantee.

Regards
Calum
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