Hacker News Reader

> The article linked here says "3D XPoint has about one thousandth the latency of NAND flash" but I don't see any actual evidence for that. The paragraph that says it is followed by a link to actual specs for a "3D XPoint" device, saying: "the Intel flash SSD has a 20-microsecond latency for any read or write operation, whereas the 3D XPoint drive cuts this to below 10 microseconds." which sounds to me more like a 2x latency improvement than a 1000x improvement.

Keep in mind that this first Optane product is a NVMe SSD. The latency overhead of PCIe and NVMe is usually about 4 microseconds minimum, as measured by reading from a SSD that has just been secure erased and thus doesn't have to actually touch the non-volatile memory in order to return a block full of zeros. This Optane SSD has a best-case latency that is only a few times better than the best case for NAND flash SSDs. This does not mean that the underlying 3D XPoint memory doesn't have a far bigger latency advantage when accessed directly by a capable memory controller, but 3D XPoint DIMMs will be next year.

The key here seems to be that performance does not drop off very much under load. DRAM cache hides latency, but only up to a point. Hiding latency is like a magic trick, and you can only hide so much before the trick starts to break down.

I'm from the nand flash industry. There seem to be a few fundamental improvements in XPoint. For one, achieving a 3X endurance improvement while keeping the same process size (dimensions of the memory cell) is new.

Given that XPoint is byte addressable is rather impressive as the circuitry and metal layers (wires) needed for this is a lot more than page addressable nand.

The true test is when they connect it directly to DIMMs versus the PCIE bus. Latency numbers there may further prove fundamental improvements in technology.

I think the byte addresability is a software layer from ScaleMP.

I have no idea, but some concern how that might affect latency.

The performance consistency that Intel claims cannot be provided by caching. The characteristics of XPoint sound vaguely similar to SLC NOR flash, but it seems like Intel would be opening themselves up to liability by outright lying.

Good to know. Have they actually said anything about Optane that would be an outright lie if Optane devices were using already-existing hardware technology?

Yes, Intel has said that it's a resistive non-flash technology.

They've said that "3D XPoint" is a resistive non-flash technology. But one of the things that makes me suspicious is that they seem to be going out of their way not to say quite explicitly, in so many words, that these Optane devices are "3D XPoint" devices.

For instance, take a look here: http://www.intel.co.uk/content/www/uk/en/architecture-and-te... -- lots of stuff about Optane, always just called Optane. There's a link at the bottom to info about "3D XPoint" but no explicit statement of the relationship between the two.

Also at the bottom of that page, a link to a video called "Revolutionizing the Storage Media Pyramid with 3D XPoint Technology". OK then. What does it say? It talks about DRAM, flash and spinning rust; then it says Intel is introducing new things; first, "DIMMs based on 3D XPoint technology" (OK, but that isn't what they're releasing right now), and then -- these are the exact words -- "Intel Optane SSDs, based on 3D XPoint technology and other Intel storage innovations" (emphasis mine). Hmmmmm.

I really hope my cynicism is misguided. But so far, everything I've seen seems to be consistent with the following story: Intel begin by announcing a new hardware technology called "3D XPoint", which works quite differently from existing flash memory and has amazing performance characteristics, and saying they're going to release products based on it under the "Optane" brand. They work on this technology but can't actually get it to work. But they need to release something. So they make the highest-performance thing they can based on existing technologies, release it under the Optane brand, and tread super-carefully to make sure they never quite say, in so many words, that this thing they're releasing actually uses the new technology they talked about before.

Now, mtdewcmu and you both say that existing tech can't actually deliver the performance Intel say this new product has, in which case it must after all be based on something genuinely new. Again, I really hope you're right. Has this performance profile -- whatever features it has that are impossible to replicate with existing technologies -- actually been demonstrated, or only claimed?

[EDITED to add:] Aha, no, looks like I'm either too cynical or not cynical enough. I found an Intel webpage -- http://www.intel.com/content/www/us/en/solid-state-drives/op... -- that actually does say, in so many words, that the P4800X uses 3D XPoint. So the story two paragraphs up isn't consistent with their current marketing materials, and I now think the story is more likely "3D XPoint doesn't work nearly as well as predicted" than "3D XPoint doesn't work at all yet and they're fudging".

It's possible the technology actually is 1000x, but it would be really dumb of Intel to release it as such, instead of milking it for years slowly creeping to 1000x.

I think like all tech they were stating the best theoretical possibility but will take a few years for them to actually get there.