Comparing Two 1TB NVMe Drives with Same NAND, Same Controller: XPG SX8200 Pro vs HP EX950

Power Management Features

Real-world client storage workloads leave SSDs idle most of the time, so the active power measurements presented earlier in this review only account for a small part of what determines a drive's suitability for battery-powered use. Especially under light use, the power efficiency of a SSD is determined mostly be how well it can save power when idle.

For many NVMe SSDs, the closely related matter of thermal management can also be important. M.2 SSDs can concentrate a lot of power in a very small space. They may also be used in locations with high ambient temperatures and poor cooling, such as tucked under a GPU on a desktop motherboard, or in a poorly-ventilated notebook.

The HP EX950 and ADATA SX8200 Pro use different firmware version numbering schemes, but they report identical power and thermal management capabilities. The only change relative to SM2262 drives and the SM2262EN engineering sample we reviewed last year is that the warning temperature threshold has been increased from 70 degrees to 75 degrees. The critical temperature threshold is still 80 degrees. The power state table hasn't changed at all, and still advertises very quick transitions in and out of both sleep states.

Note that the above tables reflect only the information provided by the drive to the OS. The power and latency numbers are often very conservative estimates, but they are what the OS uses to determine which idle states to use and how long to wait before dropping to a deeper idle state.

Idle Power Measurement

SATA SSDs are tested with SATA link power management disabled to measure their active idle power draw, and with it enabled for the deeper idle power consumption score and the idle wake-up latency test. Our testbed, like any ordinary desktop system, cannot trigger the deepest DevSleep idle state.

Idle power management for NVMe SSDs is far more complicated than for SATA SSDs. NVMe SSDs can support several different idle power states, and through the Autonomous Power State Transition (APST) feature the operating system can set a drive's policy for when to drop down to a lower power state. There is typically a tradeoff in that lower-power states take longer to enter and wake up from, so the choice about what power states to use may differ for desktop and notebooks.

We report two idle power measurements. Active idle is representative of a typical desktop, where none of the advanced PCIe link or NVMe power saving features are enabled and the drive is immediately ready to process new commands. The idle power consumption metric is measured with PCIe Active State Power Management L1.2 state enabled and NVMe APST enabled if supported.

The retail SM2262EN drives have fully functional power management, unlike the engineering sample we tested last year. Both the ADATA SX8200 Pro and HP EX950 continue the trend of Silicon Motion-based NVMe drives having excellent power management. The active idle power draw is second best among high-end NVMe drives, behind the Phison E12 controller represented here by the Corsair MP510. The Silicon Motion drives achieve better deep sleep power savings than any other NVMe drives can manage on our desktop testbed.

The downside to the excellent idle power management offered by the SM2262EN controller is that it takes quite a while to wake up—60 to 80 milliseconds, slightly longer than earlier Silicon Motion NVMe controllers, and ten times longer than what the drive's firmware claims. This can hurt responsiveness when the OS chooses to be very aggressive about transitioning the drive into lower power states based on inaccurate information about how quickly the drive can get back to work.