An introduction to the ARM server

A new generation of servers has appeared in data centers. These new servers, fitted with ARM processors, promise extremely high processing scalability while keeping power and cooling demands in check. In spite of the promise, however, ARM processors are not quite ready for wide adoption in data centers. This tip explains the current benefits and limitations of an ARM server and shows you what to look for as this technology develops.

Emergence of the ARM processor

Traditional processors are general-purpose devices capable of handling hundreds of different instructions. The problem is that general processors need hundreds of millions of transistors to handle the countless logical conditions needed to support so many instructions. This translates directly into expensive manufacturing costs: The latest Intel Xeon processors routinely cost more than $1,000 each. Even more substantially, each processor has significant power and cooling demands, which drives up the ongoing operating costs of data center servers.

By comparison, ARM processors, based on reduced instruction set computing (RISC) architectures, overcome many of these obstacles. By reducing the number of instructions, the processor is simpler, cheaper, uses far less power and runs with little (if any) substantial heat. The reduction in transistor count also improves the processor’s performance because there are fewer logical stages needed to process instructions. ARM processors are not new – they have been around for decades and can be found in smartphones, printers, digital cameras and other commercial electronic devices.

ARM processors in servers

Today, ARM processors have slowly begun to appear in some cutting-edge servers. The key factor driving the adoption of ARM processors is scalability. It’s important to understand that data centers are changing quickly. Internet-based companies, such as Google and Facebook, have discovered that it is generally more cost effective to fill data centers with vast amounts of inexpensive commodity hardware than to rely on high-performance, overpriced servers. The idea of many general-purpose servers is sometimes called “hyperscaling,” and many of the cloud service providers have also adopted the concept of hyperscaling their data centers.

While hyperscaling may offer a low-cost alternative to large, high-end servers, it also poses some problems. Perhaps the biggest issue that organizations may face as a result of hyperscaling their data centers is that of power consumption. The cost of the electricity required to keep a server online is usually trivial. However, when you multiply that cost by the hundreds of thousands of servers in a large data center, the cumulative server power cost can become staggering. And all of those servers produce heat, so cooling the data center can easily increase the cost of electricity by another 50 percent.

Organizations are discovering that ARM servers can be ideal for handling the power and cooling challenges of hyperscaling. To put the power savings into perspective, Hewlett-Packard Co. estimates that servers equipped with ARM processors could potentially consume up to 90% less power than their Intel counterparts.

While each ARM processor core typically provides less raw processing power than a traditional Intel or AMD chip, the low power and cooling requirements allow a level of server scalability that would be impossible with traditional processors. For example, the Tilara TILE-Gx family of processors can provide from 16 to 100 cores on a single chip.

In addition, a large array of processors can be assembled in a single server chassis. For example, the SeaMicro SM10000-64-HD includes dozens of Intel Atom chips, providing 768 cores in a single chassis. Compare this to a common 1U rack server with two 8-core (or even 12-core) processors. Ideally, systems like the SeaMicro SM10000-64-HD can replace 60 traditional servers with a quarter of the power and weight and one-sixth of the space.

ARM processors not quite ready

But hold onto those purchase orders. ARM technology is improving quickly, but the technology isn’t quite ready yet. Before you add an ARM server to your next technology refresh plan, it’s important to understand some of the current limitations.

First, there are currently competing ARM standards under development. ARM processors are developed differently than mainstream processors. If you buy a server with an Intel or AMD processor, then you can rest assured that the server’s processor was manufactured by Intel or AMD. If you were to purchase an ARM server or other device with an ARM processor, that processor was not manufactured by ARM Holdings. Instead, the ARM architecture is licensed to manufacturers who develop their own ARM-based CPUs.

There are several manufacturers that are developing ARM processors, and these processors will vary in capability because each manufacturer puts its own spin on the ARM standard that it has licensed.
Performance is another stumbling block that ARM processors must overcome. Current ARM processors are 32-bit, which is a poor choice for busy data center servers. However, ARM Holdings announced in October that it is developing a 64-bit core. While ARM processor licensees will invariably adopt the 64-bit license, it’s impossible to know exactly how the licensees will develop the new ARM architecture.
As one example, Applied Micro is developing an ARM-based chip known as the X-Gene that will function as a “system on a chip.” This single chip will feature multiple ARM cores (although the number of cores has not yet been released), twin 10-gigabit Ethernet ports, SATA storage control and even virtualization support. Although the X-Gene chip isn’t ready for purchase just yet, Applied Micro expects to be producing X-Gene chips by late 2012.

And finally, it’s important to consider the impact of operating systems (OSes) and workloads. ARM processors and ARM-based servers will need a suitable OS. Consumer devices may use an OS like Android or Apple’s iOS, but these are not suited for servers. Linux will support ARM, but Windows Server versions, such as 2008 R2, will not support ARM processors until (at least) the release of Windows 8. Also, current ARM processors tend to favor less-sophisticated workloads, such as Web servers, so deploying high-performance database applications on an ARM server may not be possible for some time.

The future of the ARM server is closer than you think

In spite of the challenges, highly scaled ARM servers are appearing in projects like HP’s Project Moonshot, using 2,800 Calxeda Energycore processors in a single rack. Future efforts, such as HP’s Redstone project, may look to use other ARM-type processors like the Intel Atom. When development of the hardware and software finally utilize the sheer number of ARM processors available in a single chassis, data center operators may see an extremely competitive computing platform for at least some workloads.