Re:Intel’s first Optane SSD: 375GB that you can also use as RAM
by wtallis on Sunday March 19, 2017 @09:14PM
(#13910943)
> 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.
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.