A year and a half after first publicly unveiling their new 3D XPoint non-volatile memory technology, Intel is launching the first product incorporating…
A year and a half after first publicly unveiling their new 3D XPoint non-volatile memory technology, Intel is launching the first product incorporating the new memory. The Intel Optane SSD DC P4800X is an enterprise PCIe 3 x4 NVMe SSD that Intel promises will be the most responsive data center SSD with lower latency than all of the fastest NAND flash based competitors. After months of touting 3D XPoint memory primarily with rough order of magnitude claims about its performance, endurance and cost relative to DRAM and NAND flash, and after some unexplained delays, Intel is finally providing some concrete specifications and pricing for a complete SSD that is shipping today. The information is more limited than we’re accustomed to for their NAND flash SSDs, and Intel still isn’t confirming anything about the materials or exact operating principle of the 3D XPoint memory cell.
Current computer system architectures are based around the use of DRAM as working memory and NAND flash for fast storage. 3D XPoint memory falls between the two technologies on most important metrics, so Optane SSDs bring a new dimension of complication to a server architect’s task. For most enterprise use cases, the most enticing feature of Optane SSDs over NAND SSDs is the former’s higher performance, especially reduced latencies. Aside from the gains from switching to the NVMe protocol, the latency offered by NAND flash based SSDs has been mostly stagnant or even regressed with the disappearance of SLC NAND from the market, even as throughput and capacity have grown with every generation.
The Intel Optane SSD DC P4800X is rated for a typical read or write latency under 10µs, compared to tens of microseconds for the best NAND flash based SSDs, and about 4µs minimum imposed by PCIe and NVMe transaction overhead. More impressive is how little latency degrades under less than ideal conditions. Queue depth 1 random reads are rated to remain below 30µs even while the drive is simultaneously accepting 2GB/s of sustained random writes (about 500k IOPS). Intel even specifies Quality of Service (QoS) standards for latency at the 99.999th percentile, with even QD16 random writes staying almost entirely below 200µs. A consequence of the low latency is that the P4800X can deliver full throughput at lower queue depths: the P4800X is rated to deliver maximum IOPS at QD16 while flash-based SSDs are specified for queue depths of at least 32. Unlike flash memory, the read and write performance of 3D XPoint memory is roughly equal, and this is reflected in Intel’s specifications for the P4800X.
Conspicuously missing from the performance specifications are sequential throughput. The P4800X can already use more than half of the available PCIe bandwidth with a completely random I/O workload. Rather than reassure us that the P4800X can do even better with larger transfer sizes, Intel suggests that being overly concerned with the sequential transfer speeds is a sign that you should be shopping for their 3D NAND SSDs instead. They’ll offer plenty of throughput for a far lower price.
Intel’s 3D XPoint memory is being manufactured as a 128Gb (16GB) die, slightly behind the trend for NAND flash capacities. As a result, the Optane SSD DC P4800X will start with a 375GB model and later this year be followed by 750GB and 1.
