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.

Active Idle Power Consumption (No LPM)Idle Power Consumption

With less DRAM, the 500GB Crucial MX500 saves a bit of power relative to the 1TB model when the drives are in low power state, but their active idle power consumption is essentially the same. In both scores, the Crucial MX500 is worse than many competitors and the predecessor MX300.

Idle Wake-Up Latency

The Crucial MX500 is reasonably quick to wake from idle, though the BX300 and the ADATA SU800 are substantially faster to wake up with the same SSD controller. The MX300 had been unusually slow to wake.

Mixed Read/Write Performance Conclusion
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  • PeachNCream - Friday, February 2, 2018 - link

    "..the per-die capacity of the MX500's 64-layer 3D TLC is actually lower than that of the 32L 3D TLC.."

    Why is that the case? Shouldn't doubling the number of layers lead to greater capacity and does this mean that there are more ICs per GB in the newer MX500? I'm super confused.
    Reply
  • jtd871 - Friday, February 2, 2018 - link

    "The Crucial MX500 uses Micron's 256Gb 64L 3D TLC part and consequently returns to the standard drive capacities and overprovisioning ratios, instead of the unusual configurations caused by the 384Gb die capacity in the MX300's 32L 3D TLC. The slightly lower usable capacities of the MX500 than the MX300 means the new drives have slightly higher prices on a per-GB basis, but the MSRPs are still very competitive against current street prices for the competition."

    So the new chips have more layers per package, but less overall capacity. I'll guess the 384Gb die hamstrung performance on relatively smaller-capacity drives by offering fewer memory channels for the processor to work with simultaneously. Plus, I'll guess that it was a bit of an oddball size for the algorithms to deal with.
    Reply
  • FunBunny2 - Friday, February 2, 2018 - link

    large node?
    more area dedicated to control functions?
    Reply
  • Billy Tallis - Friday, February 2, 2018 - link

    For the 32L node, IMFT was more or less prioritizing MLC use cases by making a 256Gb MLC die that could be used as a 384Gb TLC part. For the 64L node, TLC is the priority and they're making both 256Gb TLC and 512Gb TLC parts. The latter should be cheaper per GB when it is available, but would be a worse choice for small consumer drives. The 256Gb die is really tiny, which makes it more appealing to the mobile market than a lot of previous IMFT parts. Reply
  • FunBunny2 - Saturday, February 3, 2018 - link

    "making a 256Gb MLC die that could be used as a 384Gb TLC part."

    so... does this mean that NAND is all the same, and it's the controller that decides among S/M/T?? or is it the case that S can be coerced to M, and M to T, but not the other way round? is there a tute, here or elsewhere, that tells us the nittygritty about why titular NAND can/can't be used at other densities?
    Reply
  • FunBunny2 - Saturday, February 3, 2018 - link

    well, I did find one, but from 2012 (and AT: https://www.anandtech.com/show/5067/understanding-... )
    "This array can be turned into either SLC, MLC, or TLC. The actual array and transistors are equivalent in all three flash types; there is no physical difference. "

    some/many folks have been claiming that TLC, in particular, is physically different from SLC. is that now true?
    Reply
  • Kristian Vättö - Sunday, February 4, 2018 - link

    In terms of memory cell design, SLC, MLC and TLC can be the same, but the peripheral circuit design isn't (min # of latches = # of bits per cell). More bits per cell designs are also likely to have more spare/ECC bytes per page.

    In layman terms, TLC and MLC can be run as pseudo-SLC by only programming the lower page, but it's impossible to run e.g. MLC as TLC. But pseudo-SLC isn't the same thing as native SLC.
    Reply
  • Spatty - Wednesday, February 14, 2018 - link

    SLC/MLC chips are physically the same chips during the fab process. Maybe some Implant changes but die layout is the same. In Probe, circuits are blown to make them SLC or MLC.

    The referenced quote in this thread, is that a due to the usage of die vs chip/package. The chips in the images can have multiple die in one single chip/package and thus the 'density' of the chip/package changes. More layers still means more bits/mm^2.
    Reply
  • PeachNCream - Monday, February 5, 2018 - link

    Thanks Billy! It makes more sense now. Reply
  • colonelclaw - Friday, February 2, 2018 - link

    I'm wondering, would it be worth adding a PS4 Pro/'BoneX benchmark to SATA SSD reviews? The 1TB is fast becoming a worthwhile, if luxurious, upgrade for the top consoles. It may be slightly unaffordable now, but possibly not for long? Reply

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