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.
Measuring the power use of a SATA-based drive is fairly straightforward; you tap into the 5 or 12 V rail, do some multimeter work, and a bit of math. A PCI Express SSD is more difficult to get readings from. You can either use a riser card, like Igor does in our graphics card reviews, or employ a special purpose-built device.
I do the latter. Active idle is reported as a rule, so I disable the bus' sleep states to yield an equivalent to my SATA storage testing. Yes, the two PCIe-based drives can drop to lower idle power when the slot falls into a low-power condition. But we're concerning ourselves with active results in order to make the right comparison.
There is a trio of states to watch out for:
- L0 is active power/active use
- L0s is active power/idle state
- L1 is low power/slumber state
Plextor claims a .58 W idle specification, and that's pretty darned close to what we observe in PCMark 7.
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 M6e uses less power than SanDisk's A110 through PCMark 7. It also checks in just under Plextor's M6S and M6M.
After quite a bit of power testing, logging, and fiddling with Excel, we end up with the above chart.
SanDisk doesn't specify its idle consumption in the A110's documentation, though Plextor does. But it looks like both SSDs sit idle around the half-watt mark. The A110 does spent a lot more time above idle than Plextor's M6e, and after some discussion with Plextor, it appears there are ways to bring that figure down even more in certain scenarios. But PCIe power management is an entirely different beast, and I continue refining the testing.