Performance

The performance of PM is always under discussion, particularly in the case of 3D XPoint, because it is so close to release. In this case, performance has always been discussed in general terms:

• 1,000 times the performance of NAND flash
• 1,000 times the endurance of NAND flash
• 10 times the density of DRAM
• A price between flash and DRAM

In addition to the DIMM form factor, Intel is going to release 3D XPoint under the Optane brand in the form of SSDs. Recently, Intel gave a demonstration of these SSDs at the OpenWorld conference, hosted by Oracle.

The results were summarized in an article online [3].

Brian Krzanich, CEO at Intel, talked about Optane and finally gave the world some performance numbers, although they are for the Optane SSD and not the Optane DIMMs. Krzanich was demoing on what looked like a 1U two-socket server from Oracle that had two Intel Xeon E5v3 "Haswell" processors. One processor used an Intel P3700 SSD and a prototype Optane SSD. Both drives were connected to the system using NVMe [4] links to improve performance. The size of the P3700 SSD was not given, but by referencing Newegg [5], the following details were found:

• Capacity: 400GB
• Price: $909 (as of the writing of this article)
• Up to 450,000 4K random read IOPS
• Up to 75,000 4K random write IOPS
• Maximum sequential read: up to 2,700MBps
• Maximum sequential write: up to 1,080MBps

Two benchmarks or tests were shown, although the details of the tests were not given. Both tests compared the IOPS and latency using the P3700 SSD versus the Optane SSD. The results are summarized in Table 2.

Because the data path to/from the drives is the same (NVMe), the source of the differences is mostly in the drives themselves. The Optane drive is clearly much faster than the current P3700 SSD drive. Based on these results, I can't wait for the DIMM performance numbers to come out!

Summary

Persistent memory has the promise of non-volatile data storage, but with performance almost comparable to DRAM and for less cost than DRAM. A key attribute of PM is that, if for some reason, the system loses power, the data stored on the PM, perhaps on DIMMs containing the PM, is not lost as it would be with DRAM.

Persistent memory fits into a system's data storage hierarchy above permanent storage, such as disk and flash drives, but below DRAM. The non-volatile nature of PM means that it bridges the gap between storage that is either on the bus or outside the system and DRAM that is inside the system. This could be a really disruptive development for data storage. Be sure to keep a sys on it.