ARM-based servers to carve out a datacentre niche

Smooth-Stone caused a minor sensation in August when the Texas-based start-up disclosed a funding injection from some big names in the IT industry to help it develop power efficient server chips based on the ARM architecture.

The news followed an earlier announcement that ARM itself had received European Commission funding for research into more energy efficient datacentre platforms based on ARM processors.

Moves such as this highlight the growing interest in saving the energy used by servers, especially in datacentres, which now account for a small but increasing percentage of the total energy consumption in countries such as the US.

This is the background to the news that Smooth-Stone is working to develop ARM-based chips that can drive more energy efficient servers. However, the company faces a number of challenges.

ARM's chips would seem to be ideal for power-efficient servers, as the architecture has long emphasised power efficiency, leading to its almost ubiquitous presence in battery powered mobile devices and phones. But at the same time, ARM chips have lagged behind x86 processors in absolute performance for some time, so an ARM chip is no match for an Intel or AMD chip of the same clock speed.

"The ARM architecture has always been superior in performance-per-watt, but it's never been interesting in terms of raw performance until now," said Barry Evans, co-founder and chief executive of Smooth-Stone.

Evans, a former Intel executive responsible for the chip firm's ARM-based XScale processors, said that Smooth-Stone is aiming to build on that low-power design philosophy and grow absolute performance so that ARM chips can handle server workloads while retaining their performance-per-watt superiority.

Getting ARM-based servers accepted will not be an easy task in a market dominated by x86-based servers from a handful of big players, but power efficiency just might prove to be the lever that a startup could use to differentiate itself, according to Adrian O'Connell, datacentre research director at analyst firm Gartner.

"One of the dynamics of the server market is that is a very, very consolidated segment of the IT industry in terms of the vendors that play in it. Because of that, it can be really hard to achieve differentiation," he explained.

However, ARM-based servers are still likely to represent a niche part of the market, at least initially. For one thing, x86 servers are backed by a vast number of commercial software applications and services, few of which are likely to be available for the ARM architecture.

"One of the biggest issues is around the software stack, and this is one of the real advantages for x86. Given this mass of support, it is difficult to see anything that will change things in a short space of time," said O'Connell.

Where the power efficiency of the ARM chip may find a target is in large " scale-out" environments, such as internet datacentres, where applications tend to be load-balanced across a number of physical systems.

"The larger the scale of your infrastructure, the more acutely you feel any inefficiency, so that's where we're getting interest in our technology, from people who are looking for an order of magnitude improvement in efficiency," said Evans.

O'Connell agreed, saying that, in a lot of environments, the problems are not typically to do with performance.

"Often, there's actually over capacity, and the real problem is about finding a balance between power consumption and the performance of the compute equipment," he said.

Such customers may include service providers and telecoms operators, many of which have a greater level of control over their software stack because they may be building much of it themselves.

So it seems that there is a potential market for power-efficient servers, and even if it is a niche one, the rapidly expanding nature of online services means that it could represent an attractive target, if ARM-based servers can be brought to market.

Smooth-Stone itself is working on developing the processor chips, and talking with vendor partners which will actually build and sell the resulting systems.

Development still seems to be at an early stage, however, and the company is cagey about naming any potential vendors that might eventually produce ARM-based servers.

Evans was also reluctant to discuss which features the firm is designing into its chips, saying only that "we are innovating to bring a product out that will be appropriate for the server space".

However, some light may be shed on the situation by announcements made by ARM at the Hot Chips conference towards the end of August.

In a presentation by David Brash, ARM's architecture programme manager, the firm outlined extensions to its architecture that will add hardware support for virtualisation and an enlarged memory address space.

The larger address space is needed because current ARM chips use 32-bit addressing, which constrains a system to a maximum 4GB of memory.

ARM's solution, known as Large Physical Address Extension, translates 32-bit virtual addresses to a larger 40-bit physical address space.

Meanwhile, the virtualisation extensions add a new privileged execution mode for a hypervisor, plus a further mechanism for address translation between the guest operating system's memory map and the physical memory.

ARM declined to comment on whether it was working with Smooth-Stone on these extensions, but it is difficult to imagine that these features would be omitted from any forthcoming server chip based on the ARM architecture.

Additionally, the ARMv7-A architecture to which these extensions are being added already supports multi-core chip designs, and it seems probable that any server chip would be a multi-core design in order to deliver high-density compute environments in the same way as server chips from Intel and AMD.

Smooth-Stone said that it hoped to be able to share more detail on its plans in the near future, but for the meantime it is keeping its cards close to its chest.

Finally, O'Connell warned that the server market is "a pretty conservative, slow-moving industry" compared with some other areas of the IT market.

"Blades, for example, have been a high-growth area in servers for a long time, but they still represent only about 20 per cent of the total market. There can be a situation where you have a technological advantage, but it often takes a long time to ramp up," he said.