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ARM servers: not so fast

There has been a lot of chatter about deploying ARM servers in the data center recently. This page, for example, chronicles the formation of a small startup devoted to creating such systems. Most speculation about the Microsoft ARM license include this concept as well.

I joined IBM as a PowerPC Linux developer in 2001, a time when IBM was trying to use Linux to expand the market for their pSeries (now “System p”) servers. The hardware had some advantages (and disadvantages) compared to Intel servers of the day, but AIX was a limiting factor and Linux was a small but quickly growing ecosystem. It didn’t have a lot of legacy software, and it could be co-opted with minimal effort: port and maintain the Linux kernel and toolchain, and that whole juicy open source world is just a recompile away.

Although most open source software was indeed just a recompile away, it turns out that wasn’t good enough. For a long time, Linux on pSeries suffered from the lack of key enterprise applications, such as Oracle, SAP, and even IBM’s own DB2 and WebSphere suites. (In hindsight, it’s hard to fault those software providers for their reticence to port to yet another tiny platform: even when the code is just a recompile away, there is a lot more to launching a product.) As recently as 2008, IBM launched PowerVM Lx86, which performs runtime binary translation to run Linux x86 apps on Linux PowerPC servers. This was an explicit acknowledgment that PowerPC hardware sales were still being lost due to an incomplete software ecosystem. That was near the height of the PowerPC development ecosystem, when low-cost high-powered workstations were still generally available to developers.

I think the parallels with ARM are clear. Let’s say ARM servers would have advantages (power consumption) and disadvantages (poor single-thread performance, missing enterprise IO adapters) compared to traditional server hardware. Let’s also say that the ARM Linux infrastructure (kernel, toolchain, etc) is good enough or can be improved to the point that all the open source code out there “just works.” That’s still not good enough for the data center. It may not even be good enough for in-house software without dependencies on the hardware instruction set.

To be sure, there are specific use cases that could work really well for ARM servers (or MIPS servers, for that matter). Highly parallel applications (web serving tier 1) can be run on large clusters of relatively slow cores, especially if existing open source software is all that’s needed. Job postings suggest that a number of big-name companies are toying with the idea. It could happen. But ecosystems take a very long time to grow, and while we may indeed “see something out there” in less than a year, it will make far more ripples in the trade press than in the data center.

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