NVM Express, NVMe, or Non-Volatile Memory Host Controller Interface Specification (NVMHCI), is a specification for accessing solid-state drives (SSDs) attached through the PCI Express (PCIe) bus. "NVM" stands as an initialism for non-volatile memory, which is used in SSDs. As a logical device interface, NVM Express has been designed from the ground up, capitalizing on the low latency and parallelism of PCI Express SSDs, and mirroring the parallelism of contemporary CPUs, platforms and applications. By allowing parallelism levels offered by SSDs to be fully utilized by host's hardware and software, NVM Express brings various performance improvements.
NVM Express SSDs exist both in form of standard-sized PCI Express expansion cards and as 2.5-inch drives that provide a four-lane PCI Express interface through the U.2 connector (formerly known as SFF-8639). SATA Express storage devices and the M.2 specification for internally mounted computer expansion cards also support NVM Express as the logical device interface.
Historically, most SSDs used buses such as SATA, SAS or Fibre Channel for interfacing with the rest of a computer system. Since SSDs became available in mass markets, SATA has become the most typical way for connecting SSDs in personal computers; however, SATA was designed primarily for interfacing with mechanical hard disk drives (HDDs), and has become increasingly inadequate as SSDs had improved. For example, unlike hard disk drives, some SSDs are limited by the maximum throughput of SATA.
High-end SSDs had been made using the PCI Express bus before NVMe, but using non-standard specification interfaces. By standardizing the interface of SSDs, operating systems only need one driver to work with all SSDs adhering to the specification. It also means that each SSD manufacturer does not have to use additional resources to design specific interface drivers. This is similar to how USB mass storage devices are built to follow the USB mass-storage device class specification and work with all computers, with no per-device drivers needed.
The first details of a new standard for accessing non-volatile memory emerged at the Intel Developer Forum 2007, when NVMHCI was shown as the host-side protocol of a proposed architectural design that had ONFI on the memory (flash) chips side. A NVMHCI working group led by Intel was formed that year. The NVMHCI 1.0 specification was completed in April 2008 and released on Intel's web site.
Technical work on NVMe began in the second half of 2009. The NVMe specifications were developed by the NVM Express Workgroup, which consists of more than 90 companies; Amber Huffman of Intel was the working group's chair. Version 1.0 of the specification was released on 1 March 2011, while version 1.1 of the specification was released on 11 October 2012. Major features added in version 1.1 are multi-path I/O (with namespace sharing) and arbitrary-length scatter-gather I/O. It is expected that future revisions will significantly enhance namespace management. Because of its feature focus, NVMe 1.1 was initially called "Enterprise NVMHCI". An update for the base NVMe specification, called version 1.0e, was released in January 2013. In June 2011, a Promoter Group led by seven companies was formed.
The first commercially available NVMe chipsets were released by Integrated Device Technology (89HF16P04AG3 and 89HF32P08AG3) in August 2012. The first NVMe drive, Samsung's XS1715 enterprise drive, was announced in July 2013; according to Samsung, this drive supported 3 GB/s read speeds, six times faster than their previous enterprise offerings. The LSI SandForce SF3700 controller family, released in November 2013, also supports NVMe. Sample engineering boards with the PCI Express 2.0 ×4 model of this controller found 1,800 MB/sec read/write sequential speeds and 150K/80K random IOPS. A Kingston HyperX "prosumer" product using this controller was showcased at the Consumer Electronics Show 2014 and promised similar performance. In June 2014, Intel announced their first NVM Express products, the Intel SSD data center family that interfaces with the host through PCI Express bus, which includes the DC P3700 series, the DC P3600 series, and the DC P3500 series. As of November 2014[update], NVMe drives are commercially available.
In March 2014, the group incorporated to become NVM Express, Inc., which as of November 2014[update] consists of more than 65 companies from across the industry. NVM Express specifications are owned and maintained by NVM Express, Inc., which also promotes industry awareness of NVM Express as an industry-wide standard. NVM Express, Inc. is directed by a thirteen-member board of directors selected by the promoter group, which includes Avago Technologies, Cisco, Dell, EMC, HGST, Intel, Micron, NetApp, Oracle, PMC, Samsung, SanDisk and Seagate.
Comparison with AHCI
The Advanced Host Controller Interface (AHCI) interface comes with the benefit of wide software compatibility, but as a downside does not deliver optimal performance when used with SSDs connected via the PCI Express bus. As a logical interface, AHCI was developed back at the time when the purpose of a host bus adapter (HBA) in a system was to connect the CPU/memory subsystem with a much slower storage subsystem based on rotating magnetic media. As a result, AHCI introduces certain inefficiencies when used with SSD devices, which behave much more like DRAM than like spinning media.
The NVMe device interface has been designed from the ground up, capitalizing on the low latency and parallelism of PCI Express SSDs, and complementing the parallelism of contemporary CPUs, platforms and applications. At a high level, the basic advantages of NVMe over AHCI relate to its ability to exploit parallelism in host hardware and software, manifested by the differences in command queue depths, efficiency of interrupt processing, the number of uncacheable register accesses, etc., resulting in various performance improvements.:p. 17–18
The table below summarizes high-level differences between the NVMe and AHCI logical device interfaces.
|Maximum queue depth||One command queue;
32 commands per queue
65536 commands per queue
|Uncacheable register accesses
(2000 cycles each)
|Six per non-queued command;
nine per queued command
|Two per command|
and interrupt steering
|A single interrupt;
|2048 MSI-X interrupts|
and multiple threads
|Requires synchronization lock
to issue a command
for 4 KB commands
|Command parameters require
two serialized host DRAM fetches
|Gets command parameters
in one 64-byte fetch
Operating system support
- The "NVMe Windows Working Group" is an initiative from the OpenFabrics Alliance to maintain software for Microsoft Windows to use PCI Express solid state devices. The baseline Windows driver contributed to the open-source initiative was developed by several promoter companies in the NVMe workgroup, specifically IDT, Intel, and LSI.
- Microsoft added native support for NVMe to Windows 8.1 and Windows Server 2012 R2. Native drivers for Windows 7 and Windows Server 2008 R2 have been added in updates.
- Intel published an NVM Express driver for Linux. It was merged into the Linux kernel mainline on 19 March 2012, with the release of version 3.3 of the Linux kernel.
- A scalable block layer for high-performance SSD storage, known as blk-multiqueue or blk-mq and developed primarily by Fusion-io engineers, was merged into the Linux kernel mainline in kernel version 3.13, released on 19 January 2014. This leverages the performance offered by SSDs and NVM Express, by allowing much higher I/O submission rates. With this new design of the Linux kernel block layer, internal queues are split into two levels (per-CPU and hardware-submission queues), thus removing bottlenecks and allowing much higher levels of I/O parallelization.
- As of version 4.0 of the Linux kernel, released on 12 April 2015, VirtIO block driver, the SCSI layer (which is used by Serial ATA drivers), loop device driver, unsorted block images (UBI) driver (which implements erase block management layer for flash memory devices) and RBD driver (which exports Ceph RADOS objects as block devices) have been modified to actually use this new interface; other drivers will be ported in the following releases.
- Intel sponsored a NVM Express driver for FreeBSD's head and stable/9 branches. The nvd(4) and nvme(4) drivers are included in the GENERIC kernel configuration by default since FreeBSD version 10.2.
- Development work required to support NVMe in OpenBSD has been started in April 2014 by a senior developer formerly responsible for USB 2.0 and AHCI support.
- Chrome OS
- On February 24, 2015, support for booting from NVM Express devices was added to Chrome OS.
- OS X
- In the 10.10.3 update for OS X Yosemite, Apple introduced support for NVM Express. The new Retina MacBook uses NVMe as the logical device interface.
- Drew Riley (2014-08-13). "Intel SSD DC P3700 800GB and 1.6TB Review: The Future of Storage". tomshardware.com. Retrieved 2014-11-21.
- "Intel Solid-State Drive DC P3600 Series" (PDF). Intel. 2015-03-20. pp. 18, 20–22. Retrieved 2015-04-11.
- Paul Alcorn (2015-06-05). "SFFWG Renames PCIe SSD SFF-8639 Connector To U.2". Tom's Hardware. Retrieved 2015-06-09.
- Dave Landsman (2013-08-09). "AHCI and NVMe as Interfaces for SATA Express Devices – Overview" (PDF). SATA-IO. Retrieved 2013-10-02.
- Paul Wassenberg (2013-06-25). "SATA Express: PCIe Client Storage" (PDF). SATA-IO. Retrieved 2014-11-21.
- Walker, Don H. "A Comparison of NVMe and AHCI" (PDF). 31 July 2012. SATA-IO. Retrieved 3 July 2013.
- "NVM Express Explained" (PDF). nvmexpress.org. 9 April 2014. Retrieved 21 March 2015.
- "Fibre Channel Industry Association Collaborating with NVM Express, Inc. to Define New Standard for Fabric-Based Solid-State Storage Devices" (Press release).
- "Speeding up Flash... in a flash". The Inquirer. 2007-10-13. Retrieved 2014-01-11.
- "Flash new standard tips up". The Inquirer. 2008-04-16. Retrieved 2014-01-11.
- "New Promoter Group Formed to Advance NVM Express" (PDF). Press release. June 1, 2011. Retrieved September 18, 2013.
- Amber Huffman editor (October 11, 2012). "NVM Express Revision 1.1" (PDF). Specification. Retrieved September 18, 2013.
- David A. Deming (2013-06-08). "PCIe-based Storage" (PDF). snia.org. Retrieved 2014-01-12.
- Amber Huffman editor (January 23, 2013). "NVM Express Revision 1.0e" (PDF). Specification. Retrieved September 18, 2013.
- "IDT releases two NVMe PCI-Express SSD controllers". The Inquirer. 2012-08-21. Retrieved 2014-01-11.
- "IDT Shows Off The First NVMe PCIe SSD Processor and Reference Design - FMS 2012 Update". The SSD Review. 2012-08-24. Retrieved 2014-01-11.
- "Samsung Announces Industry’s First 2.5-inch NVMe SSD | StorageReview.com - Storage Reviews". StorageReview.com. 2013-07-18. Retrieved 2014-01-11.
- "LSI SF3700 SandForce Flash Controller Line Unveiled | StorageReview.com - Storage Reviews". StorageReview.com. 2013-11-18. Retrieved 2014-01-11.
- "LSI Introduces Blazing Fast SF3700 Series SSD Controller, Supports Both PCIe and SATA 6Gbps". hothardware.com. Retrieved 21 March 2015.
- Jane McEntegart. "Kingston Unveils First PCIe SSD: 1800 MB/s Read Speeds". Tom's Hardware. Retrieved 21 March 2015.
- "Kingston HyperX Predator PCI Express SSD Unveiled With LSI SandForce SF3700 PCIe Flash Controller". hothardware.com. Retrieved 21 March 2015.
- "Intel® Solid-State Drive Data Center Family for PCIe*". Intel. Retrieved 21 March 2015.
- Andy Herron (2013). "Advancements in Storage and File Systems in Windows 8.1" (PDF). snia.org. Retrieved 2014-01-11.
- Werner Fischer; Georg Schönberger (2015-06-01). "Linux Storage Stack Diagram". Thomas-Krenn.AG. Retrieved 2015-06-08.
- "Windows NVM Express". Project web site. Retrieved September 18, 2013.
- "Windows 8.1 to support hybrid disks and adds native NVMe driver". Myce.com. 2013-09-06. Retrieved 2014-01-11.
- "Update to support NVM Express by using native drivers in Windows 7 or Windows Server 2008 R2". Microsoft. 2014-11-13. Retrieved 2014-11-17.
- Matthew Wilcox (2011-03-03). "NVM Express driver". LWN.net. Retrieved 2013-11-05.
- Keith Busch (2013-08-12). "Linux NVMe Driver" (PDF). flashmemorysummit.com. Retrieved 2013-11-05.
- "IDF13 Hands-on Lab: Compiling the NVM Express Linux Open Source Driver and SSD Linux Benchmarks and Optimizations" (PDF). activeevents.com. 2013. Retrieved 2014-01-11.
- "Merge git://git.infradead.org/users/willy/linux-nvme". kernel.org. 2012-01-18. Retrieved 2013-11-05.
- "Linux kernel 3.13, Section 1.1 A scalable block layer for high-performance SSD storage". kernelnewbies.org. 2014-01-19. Retrieved 2014-01-25.
- Jonathan Corbet (2013-06-05). "The multiqueue block layer". LWN.net. Retrieved 2014-01-25.
- Matias Bjørling; Jens Axboe; David Nellans; Philippe Bonnet (2013). "Linux Block IO: Introducing Multi-queue SSD Access on Multi-core Systems" (PDF). kernel.dk. ACM. Retrieved 2014-01-25.
- "Linux kernel 3.18, Section 1.8. Optional multiqueue SCSI support". kernelnewbies.org. 2014-12-07. Retrieved 2014-12-18.
- "Linux kernel 4.0, Section 3. Block". kernelnewbies.org. 2015-05-01. Retrieved 2015-05-02.
- "Linux Multi-Queue Block IO Queueing Mechanism (blk-mq) - Device Drivers". thomas-krenn.com. 2015-06-08. Retrieved 2015-06-08.
- "Log of /head/sys/dev/nvme". FreeBSD source tree. The FreeBSD Project. Retrieved 16 October 2012.
- "Log of /stable/9/sys/dev/nvme". FreeBSD source tree. The FreeBSD Project. Retrieved 3 July 2013.
- "FreeBSD 10.2-RELEASE Release Notes". The FreeBSD Project. Retrieved 5 August 2015.
- "nvme(7D)". Oracle. Retrieved 2014-12-02.
- David Gwynne (2014-04-16). "non volatile memory express controller (/sys/dev/ic/nvme.c)". BSD Cross Reference. Retrieved 2014-04-27.
- "NVM Express » ChromeOS adds boot support for NVM Express". nvmexpress.org. Retrieved 21 March 2015.
- "4f503189f7339c667b045ab80a949964ecbaf93e - chromiumos/platform/depthcharge - Git at Google". googlesource.com. Retrieved 21 March 2015.
- "Faster 'NVM Express' SSD Interface Arrives on Retina MacBook and OS X 10.10.3". macrumors.com. Retrieved 11 April 2015.
- "ChangeLog/1.6". qemu.org. Retrieved 21 March 2015.
- "Download EDK II from". SourceForge.net. Retrieved 2014-01-11.
|Wikimedia Commons has media related to NVM Express.|
- Official website
- LFCS: Preparing Linux for nonvolatile memory devices, LWN.net, April 19, 2013, by Jonathan Corbet
- Multipathing PCI Express Storage, Linux Foundation, March 12, 2015, by Keith Busch