Lies, Damned Lies, and Specs
Watt-ergate: The SSD Power Consumption Conspiracy Exposed
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Take Intel as a case in point. The company keeps one foot in each market, actively courting consumers and IT professionals alike. Over the last few years, many people have held Intel’s SSDs in high regard, citing a good mix of performance, reliability, and price. Intel specs its 520 Series SSD at a typical active power consumption of 850 mW when running MobileMark 2007. However, last year, when we tested two 520 Series SSDs last year, we found that 850 mW was a more accurate measure of the 520’s idle power consumption. Under load, that number ballooned over 3.5W on certain workloads — over four times more power used than Intel’s specs indicate.
OCZ’s Vector SSDs are another example. OCZ lists the Vector’s active power draw at 2.25 W, and that may be a little on the conservative side according to our PCMark 7 power consumption testing. However, we noticed instances of the drive peaking at over 4.25 W, so you shouldn’t consider a drive’s active consumption rating to be its absolute ceiling. And in an enterprise environment, drives are being hammered on far more often.

Here’s the bottom line when it comes to checking spec sheets: Not all SSDs are created equal, and those consumer drives and their low active power consumption ratings are going to pull a lot of watts when you throw an enterprise-level workload at them. Related to that, you can’t assume that a consumer SSD with roughly the same throughput specs as an enterprise SSD is going to have an identical workload over the same time period. Make sure of the numbers (and workload) before making a purchase.
Also, you’ll need to perform a balancing act of sorts between an SSD’s duty cycle (which is measured in DWPD – drive writes per day), the amount work you expect the drive to perform over its life span, and the drive’s warranty. What follows these equations is how much power a drive uses to execute a certain number of operations. Returning to our example of SSD A vs. SSD B, when SSD A’s manufacturer says its drives consumes 3 W under load while SSD B’s manufacturer claims theirs uses 5 W, you have go beyond the numbers and ask questions. For example, how many watts does each drive consume to complete 20 million I/O operations?
Let’s take this further. Do you know how much energy a particular drive will use to write an outlandish amount of data, like 10 petabytes? Before you answer, we should say that the question itself is unfair because a typical consumer SSD is going to burn itself out long before approaching a lofty write total like 10 PB. So it might take two or three or even more consumer SSDs to perform the same number of writes over their lifecycle as a single enterprise SSD. In a lot of ways, it’s like trying to measure the fuel efficiency of two cars over 1 million miles, but one of the cars dies at the 250,000-mile mark while the other can drive the whole million.
For comparison, the 200 GB version of Intel’s SSD 710 has a 1.5 PB lifetime endurance rating, figured using 4 KB writes and 20% overprovisioning. Its power consumption under this scenario is 3.7 W. Now, let’s flip the script and examine an enterprise SSD, such as Seagate’s 200 GB Pulsar XT.2. The Pulsar XT.2’s typical power consumption is 4.97 W, but its write endurance clocks in at 25 PB. That hypothetical 10 PB workload mentioned above? A single Pulsar XT.2 can do that twice and get halfway through the third run over its lifecycle, whereas you’ll burn up that Intel 710 and have to replace it six times before you can cover the original 10 PB.
We also have to return to the issue of difference in workload. Although we don’t have performance results for the Intel 710 on a standardized enterprise workload, such as the Storage Performance Council’s, we’ll posit that an SSD engineered for enterprise use is going to provide superior sustained performance in a true enterprise environment. Remember our two cars faced with a million-mile road trip? We forgot to mention that it’s all off road. Now which car are you going to take, the subcompact with 13-inch tires, or the crossover SUV with AWD and all-terrain tires?

To match the hustle of a single enterprise SSD, you might need three consumer-grade drives working in unison. If we use the SSD 710 to illustrate our point, the power draw needed to match the performance of an enterprise drive is actually 11.1 W, not the 3.7 W you’d get by comparing a single consumer drive to a single enterprise drive.