The Team Group T-Force Cardea (240GB) SSD Review: Grace Under Write Pressure

Power Management

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.

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.

As with the other Phison E7 drives, the Team T-Force Cardea has a compatibility problem with out testbed when it comes to power management. Since the T-Force Cardea is intended as a desktop-only product, the overall power consumption is a very minor concern, and the heatsink eliminates any concerns about a higher idle temperature making the drive more susceptible to thermal throttling under load.

With power management that is inoperative on our testbed, none of the Phison E7 drives show more than a trivial delay when first given I/O commands after an idle period. By contrast, the Samsung 960 EVO needs an extra 5ms to come out of its sleep state.