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2018-01 NVMe and Optane Print
January 2018

Modern Compucon systems support NVMe devices and Intel Optane devices.  This article explains what they are in terms of technology.
  • NVMe stands for Non-Volatile Memory via PCI Express and is the latest interface standard for (and specifically designed for) flash memory devices, set to replace SAS and SATA (which earlier replaced SCSI and IDE respectively) for more traditional storage devices (mechanical).  It can be considered the interface of a storage device with the motherboard of a PC, but to be exact, it is the interface of a storage device via PCIe to the CPU (whether it is via a PCIe slot on the motherboard or via U.2 or M.2 physical interfaces).
  • The data transfer rate between the storage device and the motherboard is the primary motivation for NVMe.  Whilst SAS reached 12Gb per second of theoretical peak transfer rate as of writing, NVMe reaches 32Gbps for read or write by using 4 PCIe lanes on version 3 of the PCIe standard (and more if desired or needed, as it can scale with more lanes of PCIe).
  • Owing to the removal of this interface data transfer restriction, an SSD device with NVMe interface would be able to read or write at the peak speed of NAND technology.  That is, NAND medium vendors would be able to improve the technology for higher data transfer rates until reaching the interface limit. Example performance comparison of consumer devices with their respective interfaces:

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  • There are several form factors of the interface as shown in the diagram.   The top device can be inserted directly onto the PCIe slot.  The middle device goes onto the mainboard via a specific M.2 slot.  The bottom device goes into a male-female connector (U.2) which is normally off the mainboard.
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  • There are many choices of NVMe SSD on the market.  An example is Samsung PM1725 which is based on NVMe PCIe 3.0 x8 LP interface, and provides a storage size of 6.4TB, 5DWPD (disk written per day) for 5 years, transfer rates of 6000MB/s and 2000MB/s for Sequential Read and Write respectively, and Random Read and Write of 1000K and 120K IO per second respectively.
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Note: The above information has been presented in the Compucon CPD seminar on 18 October 2017
  • On top of the NVMe interface standard is the NVMe-over-Fabric standard for connecting external storage devices onto the motherboard of a PC or server. NVMe-over-Fabric standardization is going to happen over the next couple of years as it takes time to get all the interoperability worked out in the industry. Right now, the basics work but hot-plug and error recovery would take time to become bullet proof.