The Toshiba XG6 1TB SSD Review: Our First 96-Layer 3D NAND SSD
by Billy Tallis on September 6, 2018 8:15 AM ESTPower 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.
| Toshiba XG6 NVMe Power and Thermal Management Features |
|||
| Controller | Toshiba TC58NCP090GSB | ||
| Firmware | AGXA4001 | ||
| NVMe Version |
Feature | Status | |
| 1.0 | Number of operational (active) power states | 3 | |
| 1.1 | Number of non-operational (idle) power states | 3 | |
| Autonomous Power State Transition (APST) | Supported | ||
| 1.2 | Warning Temperature | 78°C | |
| Critical Temperature | 82°C | ||
| 1.3 | Host Controlled Thermal Management | Supported | |
| Non-Operational Power State Permissive Mode | Not Supported | ||
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.
| Toshiba XG6 NVMe Power States |
|||||
| Controller | Toshiba TC58NCP090GSB | ||||
| Firmware | AGXA4001 | ||||
| Power State |
Maximum Power |
Active/Idle | Entry Latency |
Exit Latency |
|
| PS 0 | 6.0 W | Active | - | - | |
| PS 1 | 2.4 W | Active | - | - | |
| PS 2 | 1.9 W | Active | - | - | |
| PS 3 | 50 mW | Idle | 1.5 ms | 1.5 ms | |
| PS 4 | 5 mW | Idle | 6 ms | 14 ms | |
| PS 5 | 3 mW | Idle | 50 ms | 80 ms | |
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.
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Spoelie - Thursday, September 6, 2018 - link
2 short questions:- what happened to the plextor M9Pe, performance is hugely different from the review back in march.
- i know this is already the case for a year or so, but what happened to the perf consistency graphs, where can i deduce the same information from?
hyno111 - Thursday, September 6, 2018 - link
M9Pe had firmware updates, not sure if it's applied or related though.DanNeely - Thursday, September 6, 2018 - link
I don't recall the details, but something went wrong with generating the performance consistency data, and they were pulled pending finding a fix due to concerns they were no longer valid. IF you have the patience to dig through the archive, IIRC the situation was explained in the first review without them.Billy Tallis - Thursday, September 6, 2018 - link
I think both of those are a result of me switching to a new version of the test suite at the same time that I applied the Spectre/Meltdown patches and re-tested everything. The Windows and Linux installations were updated, and a few tweaks were made to the synthetic test configuration (such as separating the sequential read results according to whether the test data was written sequentially or randomly). I also applied all the drive firmware updates I could find in the April-May timeframe.The steady-state random write test as it existed a few years ago is gone for good, because it really doesn't say anything relevant about drives that use SLC caching, which is now basically every consumer SSD (except Optane and Samsung MLC drives). I also wasn't too happy with the standard deviation-based consistency metric, because I don't think a drive should be penalized for occasionally being much faster than normal, only much slower than normal.
To judge performance consistency, I prefer to look at the 99th percentile latencies for the ATSB real-world workload traces. Those tend to clearly identify which drives are subject to stuttering performance under load, without exaggerating things as much as an hour-long steady-state torture test.
I may eventually introduce some more QoS measures for the synthetic tests, but at the moment most of them aren't set up to produce meaningful latency statistics. (Testing at a fixed queue depth leads to the coordinated omission problem, potentially drastically understating the severity of things like garbage collection pauses.) At some point I'll also start graphing the performance as a drive is filled, but with the intention of observing things like SLC cache sizes, not for the sake of seeing how the drive behaves when you keep torturing it after it's full.
I will be testing a few consumer SSDs for one of my upcoming enterprise SSD reviews, and that will include steady-state full drive performance for every test.
svan1971 - Thursday, September 6, 2018 - link
I wish current reviews would use current hardware, the 970 Pro replaced the 960 Pro months ago.Billy Tallis - Thursday, September 6, 2018 - link
I've had trouble getting a sample of that one; Samsung's consumer SSD sampling has been very erratic this year. But the 970 Pro is definitely a different class of product from a mainstream TLC-based drive like the XG6. I would only include 970 Pro results here for the same reason that I include Optane results. They're both products for people who don't really care about price at all. There's no sensible reason to be considering a 970 Pro and an XG6-like retail drive as both potential choices for the same purchasing decision.mapesdhs - Thursday, September 6, 2018 - link
Please never stop including older models, the comparisons are always useful. Kinda wish the 950 Pro was in there too.Spunjji - Friday, September 7, 2018 - link
I second this. I know that I am (and feel most other savvy consumers would be) more likely to compare an older high-end product to a newer mid-range product, partly to see if it's worth buying the older gear at a discount and partly to see when there is no performance trade-off in dropping a cost tier.jajig - Friday, September 7, 2018 - link
I third it. I want to know if an upgrade is worth while.dave_the_nerd - Sunday, September 9, 2018 - link
Very much this. And not all of us upgrade our gear every year or two.