Results: Power Consumption
Active Idle Power Consumption
Idle consumption is the most important power metric for consumer and client SSDs. After all, solid-state drives complete host commands quickly and then drop back down to idle. Aside from the occasional background garbage collection, a modern SSD spends most of its life doing very little. Enterprise-oriented drives are more frequently used at full tilt, making their idle power numbers less relevant. But this just isn't the case on the desktop, where the demands of client and consumer computing leave most SSDs sitting on their hands for long stretches of time.
Active idle power numbers are critical, especially when it comes to their impact on mobile platforms. Idle means different things on different systems, though. Pretty much every drive we're testing is capable of one or more low-power states, up to and including DevSlp. That last feature is a part of the SATA 3.2 host specification. And while it requires a capable SSD and a compatible platform, enabling DevSlp takes power consumption down to a very small number.
As with performance, active idle is another discipline we'd expect Adata and Crucial to measure identically in. But the M550s manage to slip in under the SP920s. Again, it's a small, yet quantifiable difference.
There is one possible explanation. Take a gander at the 1 TB drives, highlighted above. Shouldn't the 1024 GB M550 and SP920 demonstrate the exact same behavior? We know active idle is largely a function of the controller itself, since the amount of NAND on-board doesn't move the dial much. As an example, when we spent time with Intel's SSD 730, its overclocked processor affected our active idle measurement substantially.
And we see the same thing here. Compare Adata's SP920 to the M550s and we see the Crucial drives demonstrating lower power use. Could the controller be to blame? We know these are identical ASICs on the surface, but I think it's possible that Micron is reserving higher-binned 9189s for its own purposes, hitting comparable clock rates using less voltage. We reached out to Marvell for comment on this and received no answer.
PCMark 7 Average Power Consumption
If we log power consumption through a workload, even a relatively heavy one, we see that average use is still pretty close to the idle numbers. Maximum power may spike fiercely, but the draw during a PCMark 7 run is light. You can see the drives fall back down to the idle "floor" between peaks of varying intensity.
The story reported previously repeats itself here. Physically, the Adata and Crucial drives appear identical. But there are subtle differences between them not apparent based on looks alone.
Charting power over time makes it easy to see the SP920s dropping back to the 1 W+ idle floor. Peak consumption is commensurate with drive capacity.
Maximum Observed Power Consumption
Maximum power use ends up close to where we'd expect it.