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One weird trick for cheap memory... [OoB]

yawumpus
  • 21 months ago

I was flipping through Youtube when Linus of tech hints (the Youtube guy, not Torvalds. Don't know his last name) made a video on replacing DRAM with 3dXpt. Basically the idea is to use 4GB of DRAM and 16GB? of swap space on the optane drive. Some thoughts:

You'd be stuck with a single stick of RAM. This just isn't very good and probably more speed issues than you get from limiting DRAM to 4GB and paging a ton. I managed to dig up a 2GB DDR3 stick (no idea if it is an expensive specialty item or not), but 2GB might not even be part of the DDR4 [module] spec (I couldn't find anything on Amazon, and newegg's superior search methods came up empty). The youtube cheated by using two sticks and convincing windows and/or BIOS not to use it, so don't expect their results with a single stick.

I suspect 8GB and a SATA drive makes sense at this price range. 8GB is "close enough", and you will be needing both lanes for 99% of your transfers anyway (but you'll feel it every time it pages to SSD). This makes me grumpy, I thought it might be a better method for low-end systems (with 2 2GB sticks, I think it would work).

8GB and 32GB drive: cheaper than 16GB, not sure if slower. Also I have no idea if you can use 16GB as a drive partition (with a fixed page system) and still use the Intel caching software. I'd assume you could use the AMD system (assuming you had a 470 motherboard with StoreMI) to cache a SSD.

More and More: I'd assume that adding DRAM has a steep diminishing returns, and while 3dxpt will probably return even less, it won't cost so much. I'm also not really sure how many people would notice any speed improvement over a normal 512GB SATA SSD.

https://www.youtube.com/watch?v=cwy4ujt0qHM

  • Note: this is pretty much exactly what I thought of with Intel's announcement of optane/3dxpt. Replacing flash seems even further into the future, but it would be nice if it managed to cram itsway into the memory hierarchy between DRAM and SSDs. Obviously, for this strategy to really work, the Optane has to have something closer to a DDR4 interface and be read in 64 byte (or at least closer to that than 4k) chunks.

  • There's a lot of potential for a 3 tier StoreMI with this, but I'm sure that AMD cut any of those features to reduce bugs and ship on time (or at all). It would be nice to see that using the "2GB DRAM" would simply go to paging without a fuss (and quickly be read off of Optane), but I wouldn't bet on it.

  • non-enterprise Optane looks like a solution in search of a problem (the enterprise stuff makes sense if you really need that speed). Unfortunately, this scheme looks like it makes more sense than caching rotating hard drives, but Intel doesn't seem interested in other systems (quite possibly because all of them wear out the stuff to quickly. Better hope that DDR4 prices fall before your Optane wears out).

Comments

  • 21 months ago
  • 1 point

Well wouldn't you know. I post this and then Intel announces 3dxp DIMMS. Some catches:

  • Intel Xeon only.
  • 128GB minimum (obviously for servers)
  • we really don't know how this whole thing works, but the 3dxp should be byte (well, 64-bit word) accessible just like RAM.

But you really want to lose the PCIe interface before you use 3dxp as RAM. But don't hold your breath (especially for consumer gear).

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