Subject: Storage | May 30, 2018 - 07:28 PM | Allyn Malventano
Tagged: ssd, QLC, Optane DC, Optane, Intel, DIMM, 3D XPoint, 20TB
Lots of good stuff coming out of Intel's press event earlier today. First up is Optane, now (finally and officially) in a DIMM form factor!:
We have seen and tested Optane in several forms, but all so far have been bottlenecked by the interface and controller architectures. The only real way to fully realize the performance gains of 3D XPoint (how it works here) is to move away from the slower interfaces that are holding it back. A DIMM form factor is just the next logical step here.
Intel shows the new 'Optane DC Persistent Memory' as yet another tier up the storage/memory stack. The new parts will be available in 128GB, 256GB, and 512GB capacities. We don't have confirmation on the raw capacity, but based on Intel's typical max stack height of 4 dies per package, 3D XPoint's raw die capacity of 16GB, and a suspected 10 packages per DIMM, that should come to 640GB raw capacity. Combined with a 60 DWPD rating (up from 30DWPD for P4800X), this shows Intel is loosening up their design margins considerably. This makes sense as 3D XPoint was a radically new and unproven media when first launched, and it has now built up a decent track record in the field.
Bridging The Gap chart - part of a sequence from our first P4800X review.
Recall that even with Intel's Optane DC SSD parts like the P4800X, there remained a ~100x latency gap between the DRAM and the storage. The move to DIMMs should help Intel push closer to the '1000x faster than NAND' claims made way back when 3D XPoint was launched. Even if DIMMs were able to extract all possible physical latency gains from XPoint, there will still be limitations imposed by today's software architectures, which still hold many legacy throwbacks from the times of HDDs. Intel generally tries to help this along by providing various caching solutions that allow Optane to directly augment the OS's memory. These new DIMMs, when coupled with supporting enterprise platforms capable of logically segmenting RAM and NV DIMM slots, should be able to be accessed either directly or as a memory expansion tier.
Circling back to raw performance, we'll have to let software evolve a bit further to see even better gains out of XPoint platforms. That's likely the reason Intel did not discuss any latency figures for the new products today. My guess is that latencies should push down into the 1-3us range, splitting the difference between current generation DRAM (~80-100ns) and PCIe-based Optane parts (~10us). While the DIMM form factor is certainly faster, there is still a management layer at play here, meaning some form of controller or a software layer to handle wear leveling. No raw XPoint sitting on the memory bus just yet.
Also out of the event came talks about QLC NAND flash. Recently announced by Intel / Micron, along with 96-layer 3D NAND development, QLC helps squeeze higher capacities out of given NAND flash dies. Endurance does take a hit, but so long as the higher density media is coupled to appropriate client/enterprise workloads, there should be no issue with premature media wear-out or data retention. Micron has already launched an enterprise QLC part, and while Intel been hush-hush on actual product launches, they did talk about both client and enterprise QLC parts (with the latter pushing into 20TB in a 2.5" form factor).