In 2017, Toshiba was the first vendor to ship 64-layer 3D NAND in the consumer SSD market with their XG5 NVMe SSD. Now a little over a year later, the XG6 is the first SSD with 96-layer 3D NAND. The new generation of flash memory allows for better performance, improved power efficiency, and lower costs.

As the high-end tier of Toshiba's OEM SSD product line, the XG series is not officially available for retail purchase, but we think this one is pretty likely to be used as the starting point for a retail product. The last XG series drive with a retail counterpart was the XG3, the planar MLC-based sibling to the OCZ RD400. Toshiba's low-end NVMe BG series of single-chip BGA SSDs also got a retail version in the Toshiba RC100, mounted on a M.2 2242 card. Retail and OEM versions usually have some firmware differences and occasionally one or two significant hardware differences such as 19nm vs 15nm MLC for the XG3 and RD400, or 30mm vs 42mm card length for the BG3 and RC100. Despite those differences, OEM SSDs are usually a pretty accurate preview of later retail versions.

OEM SSDs are usually not designed with maximum performance as the primary goal. OEMs prefer to have the option of sourcing more than one SSD for use in each of their systems, and they aren't interested in paying a large premium for some of their drives to be substantially faster than the rest. That said, for certain systems OEMs do want a true high-end drive, and the bar for that gets higher with every generation. Late last year, Toshiba introduced a higher performing XG5-P variant with a focus on better performance for more intensive workloads and benchmarks that exercise the full drive capacity with lots of random access. The XG6 is only intended to directly replace the XG5, but in light of the performance increases it brings, the 1TB XG5-P is now obsolete. The 2TB XG5-P may stick around for a while longer simply because the XG6 is not available in capacities above 1TB.

The new 96-layer BiCS4 3D TLC NAND used by the Toshiba XG6 is the most advanced flash memory currently shipping, but relative to the 64-layer BiCS3 that currently makes up most of the NAND volume from Toshiba and SanDisk it is more of an incremental update rather than revolutionary change. The increased layer count improves density but the TLC die capacities are still 256Gb and 512Gb. The I/O interface has been upgraded to the Toggle NAND 3.0 standard, with speeds in the 667-800MT/s range compared to the 400-533MT/s speeds used by earlier 3D NAND from Toshiba. The speed bump brings Toshiba's NAND up to par for its current competition, but it will soon be eclipsed by the 1.4GT/s Toggle 4.0 interface that Samsung's upcoming 96L V-NAND will be using. (Though it remains to be seen whether such a big increase in interface speed will have much effect on overall drive performance when drives will still be limited to PCIe 3.0 x4 speeds for another generation or two.) The NAND interface voltage has also dropped from 1.8V to 1.2V, so the higher I/O speed shouldn't have much impact on power efficiency.

Toshiba OEM NVMe SSD Comparison
Model XG6 XG5 XG5-P BG3 XG3
Retail Counterpart None RC100 RD400
Capacities 256GB, 512GB, 1024GB 1TB, 2TB 128GB, 256GB, 512GB 128GB, 256GB, 512GB, 1024GB
Form Factor M.2 2280 M.2 2230 M.2 2280
Host Interface PCIe 3.1 x4 PCIe 3.1 x2 PCIe 3.1 x4
Protocol NVMe 1.3a NVMe 1.2.1 NVMe 1.1b
NAND Flash Toshiba 96L BiCS4 3D TLC Toshiba 64L BiCS3 3D TLC Toshiba 19nm MLC
Sequential Read 3180 MB/s 3000 MB/s 3000 MB/s 1500 MB/s 2400 MB/s
Sequential Write 2960 MB/s 2100 MB/s 2200 MB/s 800 MB/s 1500 MB/s
Random Read 355k IOPS   320k IOPS    
Random Write 365k IOPS   265k IOPS    
Power Read 4.2 W 4.5 W 4.9 W 3.3 W 5.5 W
Write 4.7 W 3.4 W 3.2 W 6.4 W
Idle 3 mW 3 mW 3 mW 5 mW 6 mW
TCG Opal Encryption Optional No

Aside from the upgrade to a new generation of 3D NAND, not much has changed from the XG5. The Toshiba XG6 is still using the same TC58NCP090GSB 8-channel controller as the XG5, but with another year's worth of firmware development. The use of an existing controller probably helped Toshiba get the XG6 out the door sooner and ensure they could be first to ship drives with 96L NAND, but it is possible that the XG6's performance is being held back a bit by the older controller. The controller is not really obsolete yet since it is still one of the most power-efficient NMVe controllers available, but the new in-house controller Western Digital debuted earlier this year gets more performance out of the same flash while usually offering similar power efficiency. Toshiba will need a new controller next year in order to keep the XG series in the high-end segment.

The basic layout of the XG6 has not changed from the XG5, though the power delivery components have been modified slightly, likely to accommodate the lower voltage for the NAND interface. The XG6 is another single-sided design to maximize compatibility with the thinnest notebook computers. Our 1TB sample has two NAND packages each containing eight 512Gb BiCS4 3D TLC dies. Toshiba is using 256Gb dies on at least some of the smaller capacities, but they won't say specifically whether it's just the 256GB model or also the 512GB model. Either way, it's nice that they are willing to use the slightly less cost-effective low-capacity parts for smaller drives in order retain most of the performance by keeping all 8 of the controller's channels populated.

Our XG6 came with an unusual rigid plastic label that gives it the polished appearance of a retail product, but doesn't actually serve as the heatspreader it resembles. Thanks to the power efficiency of Toshiba's controller, heat shouldn't be a problem at all.

The Competition

We don't get OEM SSDs in for review very often. Toshiba is only really sampling the XG series because it is where their 64L and 96L NAND have debuted, and they haven't had retail versions ready to sample instead. Most of the other drives we have to compare the XG6 against are retail models, but most of them have OEM counterparts based on the same hardware and similar or identical firmware. For example, the WD Black is closely related to the WD SN720 that was announced slightly earlier but wasn't sampled for review.

AnandTech 2018 Consumer SSD Testbed
CPU Intel Xeon E3 1240 v5
Motherboard ASRock Fatal1ty E3V5 Performance Gaming/OC
Chipset Intel C232
Memory 4x 8GB G.SKILL Ripjaws DDR4-2400 CL15
Graphics AMD Radeon HD 5450, 1920x1200@60Hz
Software Windows 10 x64, version 1709
Linux kernel version 4.14, fio version 3.6
Spectre/Meltdown microcode and OS patches current as of May 2018
AnandTech Storage Bench - The Destroyer
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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.

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