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Understanding SSD Technology: NVMe, SATA, M.2

The Benefits of NVMe

NVMe technology provides superior storage, superior speed and superior compatibility. Because NVMe utilizes PCIe sockets, it transfers 25x more data than the SATA equivalent. Along with more data, NVMe’s commands are 2x faster than that of AHCI drivers. In addition, NVMe input/output operations per second (IOPS) exceeds 1 million and is up to 900% faster compared to AHCI drives. NVMe also communicates directly with the system CPU giving it incredible speeds due to its compatibility. NVMe drives work with all major operating systems regardless of form factor.

NVME LogoNVMe (Non-Volatile Memory Express) is a communications interface and driver that takes advantage of the increased bandwidth PCIe has to offer. It’s designed to increase performance and efficiency while making a broad range of enterprise and client systems interoperable. NVMe was designed for SSDs and communicates between the storage interface and the system’s CPU using high-speed PCIe sockets without the limitations of form factor. 

The NVMe protocol utilizes parallel, low-latency data paths to the underlying media like high performance processor architectures. This offers significantly higher performance and lower latencies compared to SAS and SATA protocols. NVMe can support multiple I/O queues, up to 64K with each queue having 64K entries. This allows input/output tasks to transfer more data faster than older storage models using legacy drivers such as AHCI (Advanced Host Controller Interface). Because NVMe is designed specifically for SSDs, it will eventually become the new industry standard.

SSD Storage: SATA vs PCIe

Data buses transfer data within a system and when NAND-based SSDs first came out, it was clear to the industry that a new bus and protocol were necessary.

  • The first SSDs were relatively slow which made it convenient to use the existing SATA storage infrastructure. Even though the SATA bus has evolved to 16Gbps, nearly all commercial implementations of the SATA bus remain 6Gbps.
  • PCIe 3.0’s total throughput is 16Gbps while PCIe 4.0 has double the throughput of PCIe 3.0. It offers up to 16 lanes and can transfer data up to 32,000MB/s while SATA III transfers only up to 600MB/s.

The decision to leverage an existing higher-bandwidth bus technology replaced SATA protocols with PCIe technology. PCIe storage came before NVMe by a few years but since previous solutions were bottlenecked by older data transfer protocols such as SATA and AHCI, it couldn’t be used to its full potential until recent years. NVMe was the solution for the bottlenecks and removes limitations by offering low-latency commands and 64K queues. The multiple queues allow faster data transfers because data is written to SSDs in a scattered fashion using chips and blocks rather than being written on spinning disks like hard drives.

Communication Drivers: AHCI vs NVMe

Communication drivers are used by operating systems to communicate data with storage devices. NVMe drivers are faster than AHCI drivers which are commonly found in SATA interfaces.

  • NVMe is designed specifically for SSDs with flash technology making it faster than AHCI drivers which was designed for common hard drives with spinning disk technology.
  • While NVMe has 64K command queues and can send 64K commands per queue, AHCI only has one command queue and can only send thirty-two commands per queue.
  • With AHCI drivers, commands utilize high CPU cycles with a latency of 6 microseconds while NVMe driver commands utilize low CPU cycles with a latency of 2.8 microseconds.

The NVMe driver communicates directly with the system CPU but the AHCI must communicate with the SATA controller. The AHCI has IOPS (Input/Output Operations Per Second) up to 100K while the NVMe has IOPS over 1 million. IOPS (Input/Output Operations Per Second, pronounced i-ops) is a common performance measurement used to benchmark computer storage devices.

NVMe SSD Form Factors

NVMe SSDs come in a variety of form factors but they get specific depending on the use case or application.

  • Personal/Client products use BGA and M.2 form factors.
  • Data Center/Server applications use M.2, U.2, U.3, and EDSFF form factors.

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There are developing standards and efforts within the EDSFF (Enterprise and Data Center SSD Form Factor) which offers a dynamic range of form factors and standards that share the same protocol (NVMe), the same interface (PCIe), and use their own edge connector (SFF-TA-1002), pinout and functions (SFF-TA-1009).

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