Very low-power scale-out servers — it’s an idea whose time has come. A few weeks ago Intel announced it was doing Microslice servers: Intel Seeks new ‘microserver’ standard. Rackable Systems (I may never manage to start calling them ‘SGI’ – remember the old MIPS-based workstation company?) was on this idea even earlier: Microslice Servers. The Dell Data Center Solutions team has been on a similar path: Server under 30W.

Rackable has been talking about very low power servers as physicalization: When less is more: the basics of physicalization. Essentially they are arguing that rather than buying, more-expensive scale-up servers and then virtualizing the workload onto those fewer servers, buy many smaller servers. This saves the virtualization tax which can run 15% to 50% in I/O intensive applications and smaller and low-scale servers can produce more work done per joule and better work done per dollar. I’ve been a believer in this approach for years and wrote it up for the Conference on Innovative Data Research last year in The Case for Low-Cost, Low-Power Servers.

I’ve recently been very interested in the application of ARM processors to web-server workloads:

· Linux/Apache on ARM Processors

· ARM Cortex-A9 SMP Design Announced

ARMs are an even more radical application of the Microslice approach.

Scale-down servers easily win on many workloads when looking at work done per dollar and work done per joule and I claim, if you are looking at single dimensional metrics, like performance, you aren’t looking hard enough. However, there are workloads where scale-up wins. They are absolutely required when the workload won’t partition and scale near linearly. Database workloads are classic examples of partition-resistant workloads that really do often run better on more-expensive, scale-up servers.

The other limit is administration. Non-automated IT shops believe they are better off with fewer, more-expensive servers although they often achieve this goal by running many operating system images on a single server. Given that the bulk of administration is spent on the software stack, it’s not clear that this approach of running the same number of O/S images and software stacks on a single server is a substantial savings. However, I do agree that administration costs are important at low-scale. If, at high-scale, admin costs are over 10% of overall operational costs, go fix it rather than buying bigger, more expensive servers.

When do scale-up servers win economically? 1) very low-scale workloads where administration costs dominate, and 2) workloads that partition poorly and suffer highly-sub-linear scale-out. Simple web workloads and other partition-tolerant applications should look to scale-down severs. Make sure your admin costs are sub-10% and don’t scale with server count. Then use work done per dollar and work done per joule and you’ll be amazed to see scale-down gets more done at lower cost and lower power consumption.

2010 is the year of the low-cost, scale-down server.


James Hamilton



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