High speeds with light loads—and consistent performance nearly everywhere
Because of these properties, Optane products have exceptionally low latency for persistent storage devices, and it's that characteristic—not sequential performance—that you'll hear emphasized in Intel's marketing materials for Optane. In fact, Intel won't be providing sequential performance specifications for Optane SSDs in official materials, because it believes those figures will be misused by its competitors to misrepresent Optane SSD performance compared to NAND.
Intel justifies this stance by noting that NAND SSD makers (itself included) can only deliver their specified performance numbers by testing workloads with unrealistically high queue depths like 128. Outside of those synthetic situations, the company claims its internal testing shows that even heavy server workloads often don't exceed QD16, and that will be especially true of Optane thanks to its symmetrical read and write performance. That symmetry means read requests won't be held up behind higher-latency writes, as they would be with NAND controllers. In fact, Intel says that those who need large sequential numbers at high queue depths should just use NAND devices.
Instead, the Optane SSD DC P4800X really shines in low-queue-depth random workloads. Compared to even the DC P3700 NAND SSD, Intel says the P4800X offers eight times the performance of the NAND drive at QD1, and that lead still holds at about five times the random performance of NAND as queue depths increase. In fact, the P4800X saturates at about QD12, and Intel says that the only characteristic that changes with deeper queues on this drive is its service latency.
That's not the end of the P4800X's performance benefits, however. Not only does the Optane drive's low-QD performance shine compared to NAND, the consistency of that performance could also be revolutionary compared to today's SSDs. TR readers are already quite familiar with the importance of 99th-percentile performance thanks to our Inside the Second graphics-card benchmarking methods (themselves inspired by the use of that metric in server benchmarking), and Intel is deploying a similar measure to demonstrate the performance of the P4800X.
Intel has devised what it claims is a better method of demonstrating the unique benefits of Optane in those worst-case scenarios: the "write pressure" test, in which the latency for a read operation is measured while the drive is servicing a sustained quantity of write IOPS. The stairstep line in the rather complex chart above shows the random write IOPS rate in MB/s. The squiggly blue line is the average read response time in microseconds for the DC P3700, while the orange line near the x-axis demonstrates the average read response time for the DC P4800X.
Although it's not shown in the write pressure graph, Intel says it saw similar average read response times for the P4800X all the way out to a remarkable 2GB/s of random write pressure. That consistency is a huge deal for Optane application performance, just as a low 99th-percentile frame time is for gaming. Even if one considers 99.999% response time for the DC P4800X on the logarithmic scale above, it's still well below the average response time for the NAND DC P3700.
As just one example of the way the DC P4800X can boost application performance, Intel presented an example case of a two-server MySQL setup with a database too large to fit in RAM. Running Sysbench 0.5 with a 70-30 read-write split, and with the data stored on a 400GB Intel DC P3700, the rack could handle only 1395 transactions per second. With the 375GB DC P4800X, that number soars to 16480 transactions per second with similar 99th-percentile latency. That's an impressive performance boost from mostly the same hardware.