Intel's new 3D NAND will cost less, but may offer effectively similar write speeds

Subject: Editorial, Storage
Manufacturer: PC Perspective
Tagged: ssd, nand, Intel, flash, 3d

It has become increasingly apparent that flash memory die shrinks have hit a bit of a brick wall in recent years. The issues faced by the standard 2D Planar NAND process were apparent very early on. This was no real secret - here's a slide seen at the 2009 Flash Memory Summit:

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Despite this, most flash manufacturers pushed the envelope as far as they could within the limits of 2D process technology, balancing shrinks with reliability and performance. One of the largest flash manufacturers was Intel, having joined forces with Micron in a joint venture dubbed IMFT (Intel Micron Flash Technologies). Intel remained in lock-step with Micron all the way up to 20nm, but chose to hold back at the 16nm step, presumably in order to shift full focus towards alternative flash technologies. This was essentially confirmed late last week, with Intel's announcement of a shift to 3D NAND production.

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Intel's press briefing seemed to focus more on cost efficiency than performance, and after reviewing the very few specs they released about this new flash, I believe we can do some theorizing as to the potential performance of this new flash memory. From the above illustration, you can see that Intel has chosen to go with the same sort of 3D technology used by Samsung - a 32 layer vertical stack of flash cells. This requires the use of an older / larger process technology, as it is too difficult to etch these holes at a 2x nm size. What keeps the die size reasonable is the fact that you get a 32x increase in bit density. Going off of a rough approximation from the above photo, imagine that 50nm die (8 Gbit), but with 32 vertical NAND layers. That would yield a 256 Gbit (32 GB) die within roughly the same footprint.

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Representation of Samsung's 3D VNAND in 128Gbit and 86 Gbit variants.
20nm planar (2D) = yellow square, 16nm planar (2D) = blue square.

Image republished with permission from Schiltron Corporation.

It's likely a safe bet that IMFT flash will be going for a cost/GB far cheaper than the competing Samsung VNAND, and going with a relatively large 256 Gbit (vs. VNAND's 86 Gbit) per-die capacity is a smart move there, but let's not forget that there is a catch - write speed. Most NAND is very fast on reads, but limited on writes. Shifting from 2D to 3D NAND netted Samsung a 2x speed boost per die, and another effective 1.5x speed boost due to their choice to reduce per-die capacity from 128 Gbit to 86 Gbit. This effective speed boost came from the fact that a given VNAND SSD has 50% more dies to reach the same capacity as an SSD using 128 Gbit dies.

Now let's examine how Intel's choice of a 256 Gbit die impacts performance:

  • Intel SSD 730 240GB = 16x128 Gbit 20nm dies
    • 270 MB/sec writes and ~17 MB/sec/die
  • Crucial MX100 128GB = 8x128Gbit 16nm dies
    • 150 MB/sec writes and ~19 MB/sec/die
  • Samsung 850 Pro 128GB = 12x86Gbit VNAND dies
    • 470MB/sec writes and ~40 MB/sec/die

If we do some extrapolation based on the assumption that IMFT's move to 3D will net the same ~2x write speed improvement seen by Samsung, combined with their die capacity choice of 256Gbit, we get this:

  • Future IMFT 128GB SSD = 4x256Gbit 3D dies
    • 40 MB/sec/die x 4 dies = 160MB/sec

Even rounding up to 40 MB/sec/die, we can see that also doubling the die capacity effectively negates the performance improvement. While the IMFT flash equipped SSD will very likely be a lower cost product, it will (theoretically) see the same write speed limits seen in today's SSDs equipped with IMFT planar NAND. Now let's go one layer deeper on theoretical products and assume that Intel took the 18-channel NVMe controller from their P3700 Series and adopted it to a consumer PCIe SSD using this new 3D NAND. The larger die size limits the minimum capacity you can attain and still fully utilize their 18 channel controller, so with one die per channel, you end up with this product:

  • Theoretical 18 channel IMFT PCIE 3D NAND SSD = 18x256Gbit 3D dies
    • 40 MB/sec/die x 18 dies = 720 MB/sec
    • 18x32GB (die capacity) = 576GB total capacity

​​Overprovisioning decisions aside, the above would be the lowest capacity product that could fully utilize the Intel PCIe controller. While the write performance is on the low side by PCIe SSD standards, the cost of such a product could easily be in the $0.50/GB range, or even less.

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In summary, while we don't have any solid performance data, it appears that Intel's new 3D NAND is not likely to lead to a performance breakthrough in SSD speeds, but their choice on a more cost-effective per-die capacity for their new 3D NAND is likely to give them significant margins and the wiggle room to offer SSDs at a far lower cost/GB than we've seen in recent years. This may be the step that was needed to push SSD costs into a range that can truly compete with HDD technology.

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November 27, 2014 | 07:04 AM - Posted by Chaitanya Shukla

I believe Samsung has pushed all NAND flash mamufacturers towards 3D process. Even toshiba it seems will be making 3D Nand flash chips in 2015. Samsung caught the competition sleeping with release of 850pro ssd.

November 27, 2014 | 09:49 AM - Posted by drB (not verified)

Mm!fujtsu 240 gb ssd (using Intel SLC 25nm flash )is way better,and laptop sized!its benefit?almost 3 time the life of the Samsung unit mentionned here (vnand)

November 28, 2014 | 09:25 PM - Posted by Laststop (not verified)

no consumer needs the endurance of SLC flash. The HUGE price premium for SLC is hugely wasted on consumer workloads. You need very heavy enterprise database workloads that slam the drive with many multiple full drive rewrites per day to make SLC economical.

November 28, 2014 | 09:22 PM - Posted by Laststop (not verified)

They say intel is focused on the price more than the performance I find that hard to believe though Intels SSD while being extremely reliable have also been notoriously the most expensive. The speed of current modern day SSD's is so good that even the low end ones like the crucial mx100 still offer more than enough speed for normal consumer uses. If intel can really bring the price down by a huge margin with this 3d nand say to something like 25 cents per GB and bring along their rock solid reliability then even though you will have to buy 512GB or larger to get the full write speed at 25 cents per GB we are talking 128 dollars for a 512GB drive. So I would have no problem spending that. Hell even if it was a more realistic 35 cents per GB that would still only be 180 dollars for a 512GB drive.

So if intel is truly focusing on price per GB then 35 cents per GB should be attainable as we already have some people slightly under 50 cents per GB. And if they do get this price down there then the fact you need to buy 512GB to get full use of the write speed thats not really a problem.

December 1, 2014 | 12:31 PM - Posted by BBMan (not verified)

The warranty is what sells me. It's their bet that their product will be there before it expires or they have to pony up for another drive. A 10 year warranty tells me what I need to know about reliability. Drives from 10 years ago are largely not even on the market anymore and are mostly noisy junk. So it may cost me some today, but I'm not going to worry about it 10 years from now- let alone 3. It will be interesting to see how this end of it measures up.

December 2, 2014 | 04:58 PM - Posted by Anonymous (not verified)

>Crucial MX100 128GB = 8x128Gbit 16nm dies

MX100 128GB is not using 16nm dies. Even Crucial themselfs say so (its older 20nm flash).

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