I've been out of the loop for a while datacenter-wise, and so fail to see the immediate value here.
Are these servers running virtualized instances?
Are they much cheaper as far as $/request or watt/request (or other efficiency metric?
How do they compare to a slice of an Intel server, which has the benefit of a more mature environment?
Current ARM server chips are much worse than Intel chips on the performance/watt metric [1]. The datacenter play would necessarily have to target consumers with low performance needs and offer them a better price. That would be tough because you have to compete against the already-cheap $5/server/mo Intel market.
AMD's SeaMicro was arguably the best shot at offering an alternate ARM-server commoditization model. AMD shut down SeaMicro in April [2].
ARM has typically been more efficient, for both heat and power consumption, while losing out on computational power.
That's enabled people to cram significantly more processing cores into a server rack. 4 years ago HP release a server line with 288 quad-core ARM processors in 4U, for a total of 1152 cores. Obviously that introduces the complexity of needing code that is suited to massive parallelism. Each processor there took up just 1.5 watts idle, 5 watts under load. By comparison the Atom from Intel at the time had comparable performance, but consumed 8.5 watts, just over 70% more, and didn't idle to as low consumption.
There are a number of problems that are significant with large scale data-centre operations, but power consumption and heat generation are way up there at the top. In theory a data-centre filled with ARM based servers would give you comparable performance, but with cheaper electrical and climate control bills.
The emphasis there is on "in theory" :) The reality at the moment is that companies have spent years trying to get ARM based, massive core count servers to be a thing, and it hasn't really worked out. Switching processor architectures is never something that can be done lightly. Software has to be compiled and supported provided for it, and isn't necessarily tuned for the ARM architecture. The x86 architecture's performance characteristics have been really well understood, and software likely designed with those characteristics in mind.
Historically ARM has also lacked Windows server support, and had very variable quality linux support (not helped by every Tom, Dick and Harry SoC company do the darnedest things in pursuit of creating 'value'.) As far as I've heard, they've since done (or started on?) a huge restructuring of the ARM path in the kernel to clean up the mess and provide significantly better customisation opportunities.
In part it has also seemed like a case of "no one ever got fired for buying IBM". You've only got a certain budget, do you gamble on an unproven (to you) architecture, or stick the the tried and tested Intel?
Twirrim: ARM has typically been more efficient, for both heat and power consumption, while losing out on computational power.
i_have_to_speak : Current ARM server chips are much worse than Intel chips on the performance/watt metric.
It's hard to square these two statements. It might depend on how you define "efficiency". If efficiency is the amount of energy to perform a calculation, I don't think ARM is more efficient. This paper from a couple years ago concludes that ISA is no longer a defining factor: http://www.embedded.com/design/connectivity/4436593/Analysis...
Separately, this is an excellent article comparing recent generations of Intel against each other, showing that although power use has been going up, "instructions per cycle" has been going up even faster, resulting in a net improvement in energy efficiency: http://kentcz.com/downloads/P149-ISCA14-Preprint.pdf
I wonder if the question we ought to be asking is "How idle is your server farm"? ARM still uses significantly less power than Intel chips do when idle. If your fleet is working hard all the time, it would be a no-brainer to go with Intel. What if your fleet spends 50% of the time not working? 70%? There presumably is some tipping point there.
If my server farm is idle any significant amount, I'm going to take those servers offline. If I need capacity, I'll spin up some cloud instances in the short term, and I'll bring my own servers online until I'm at an appropriate idle/busy metric.
I suspect that the days of 99% idle servers are long gone. I suspect that utilization is probably above 70%.
I suspect there is a tipping point, but that it's probably much lower than you suggest: maybe 10-25% of a single core, thus some single digit percentage of the entire processor.
Modern Intel processors can shut down unneeded cores almost completely, and frequency scaling gives you another range of efficient power reduction. It's only when you get lower than that that you are losing significant power at 'idle'.
Unlike a small battery powered device, I'd guess that the difference in idle power for the CPU is never going to be the deciding factor, as keeping the non-CPU rest-of-the-machine running will dwarf the difference. What workload would you envision as having the greatest advantage? Maybe if you were running a single instance per dedicated core?
Are these servers running virtualized instances? Are they much cheaper as far as $/request or watt/request (or other efficiency metric? How do they compare to a slice of an Intel server, which has the benefit of a more mature environment?