The Toshiba XG6 1TB SSD Review: Our First 96-Layer 3D NAND SSD

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 Toshiba XG6 supports most of the NVMe power and thermal management features save for the relatively obscure and recent non-operational power state permissive mode to control background processing during idle time. The XG6 is a bit unusual in providing three idle states instead of just two, but the deepest state is probably not worth using very often due to its higher transition latency and minimal power power savings relative to the intermediate PS4 idle state.

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 active idle power consumption of the Toshiba XG6 is slightly higher than the XG5 but still in the normal range for high-end NVMe drives. However, Silicon Motion and Phison have both managed to reach active idle power levels that are well under 1W instead of slightly higher, so Toshiba does have some room for improvement in power efficiency. The 110mW idle power we measured is decent for a NVMe drive, but substantially higher than the Silicon Motion controllers that manage the rare feat of successfully making use of their deepest idle state even on our desktop testbed.

The idle wake-up latency of the Toshiba XG6 is substantially higher than the XG5 and is comparable to that of the Silicon Motion-based drives that lead in our idle power consumption measurements. As long as the Toshiba XG6 is no slower to wake up in a notebook system where it successfully reaches its deepest power state, this latency shouldn't be a problem. Desktop systems would probably not be using the deepest idle state very often, so the wake-up should usually be much lower than the 52ms measured here.