Solid State Drive Form Factors

Solid-state drives (SSDs) are commonly used in client, hyperscale and enterprise compute environments.  They typically come in three flavors:  NVMe™, SAS, and SATA. Since SSDs are made from flash memory, they can be built in many different form factors. This resource guide is designed to provide information on the most common and current SSDs in their various form factors. In addition to the form factor dimensions, information such as use case, interface, protocol, and mechanical/electrical and connector specifications are provided.

Click on the names below to learn more about the many different SSD sizes and formats in a variety of form factors: 

• EDSFF
• M.2
• 2.5-inch (U.2)
• Add In Cards

EDSFF

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E1.L, EDSFF 1U Long

^{Illustrations left to right:  E1.L 9.5mm (courtesy of Intel); E1.L 18mm (courtesy of Intel)}

E1.L is a form factor that was developed to maximize capacity per drive and per rack unit in a 1U server or storage array (JBOD, JBOF), with superior manageability, serviceability, and thermal characteristics vs traditional form factors that were designed for rotating media. There are options for x4 or x8 lanes of PCIe while fitting vertically in a 1U chassis to allow for scalable bandwidth per drive, as well as options for 9.5 or 18mm heat sinks for various power and thermal environments (25W and 40W respectively). It improves data center serviceability, and is designed to be hot pluggable and front access serviceable with LEDs built into an integrated enclosure.

Use Cases

E1.L is optimized for high-capacity and dense storage use cases. High capacity per rack unit can improve data center TCO by offering storage consolidation and more power efficient storage (TB/W).

Dimensions

E1.S, EDSFF 1U Short

^{Illustrations left to right:  E1.S 5.9mm (courtesy of SMART Modular Systems); E1.S Symmetric Enclosure (courtesy of Intel); E1.S Asymmetric Enclosure (courtesy of KIOXIA)}

E1.S is a flexible, power efficient building block for hyperscale and enterprise compute nodes and storage. The M.2 110mm was popular in hyperscale data centers due to the low-cost structure, flexibility, and scalability of multiple drives per server – but had challenges in hotplug / serviceability, thermals and overheating, and scaling to high capacities. E1.S solves those problems while maintaining the small form factor; E1.S is a small form factor being just a bit longer than M.2 but wider to accommodate more media (NAND) packages for increase capacity per drive. It fits vertically in a 1U chassis, similar to E1.L. The specification for E1.S 5.9mm has four standard mounting holes for heat sinks or carriers.

Different variants of E1.S offer improved flexibility for power, performance, scalability, and thermal efficiency. The latest version of E1.S offers a new optional symmetrical enclosure of 9.5mm width (similar to E1.L) that allows scalability up to 20W and x8 PCIe if required. Mainstream SSDs are still expected to be only PCIe x4, but the PCIe x8 support in the form factor allows use of other devices that need higher bandwidth.

The 15mm and 25mm asymmetrical enclosures offers a tradeoff of fewer drives per rack unit but improved power and performance per drive. At similar power per drive, the 15mm and 25mm enclosures offer improved cooling and thermal performance, decreasing the required airflow.

Use Cases

• Cloud compute servers
• OEM 1U performance server

Dimensions

EDSFF E3.S and E3.L

^{Illustrations left to right: EDSFF E3 Group (SNIA specifications); E3.S (courtesy of KIOXIA)}

EDSFF E3 is a family of form factors designed to update and replace the traditional U.2 2.5-inch form factor in servers and storage systems.  The different versions share the same height (76mm), and have commonality in length (112.75mm and 142.2mm) and width (7.5mm and 16.8mm).  These hot-pluggable drives are designed more optimally for flash density of the SSD and system chassis.  The E3 family connector is designed for x4 to x16 PCIe lanes and power envelopes up to 70W.  All versions should be slot/connector compatible and are designed to be front accessible.  Designed for future servers and storage systems, EDSFF E3 will accommodate next generations of PCI Express and can accommodate device types such as GPUs and NICs.

Where Used

• The primary usage is SSDs, but E3 is big enough to accommodate a broader range of device types.
• The E3 form factor allows for x4, x8, or x16 PCIe host interface.

Dimensions

M.2

M.2 is a form factor specification for internally mounted SSDs.  Formerly known as Next Generation Form Factor (NGFF), M.2 supports PCIe, SATA and USB interfaces and comes in various widths and lengths.  It also has keying notches on the edge connector to designate various interface or PCIe lane configurations.  M.2 is smaller than the typical 2.5” form factor SSD and is typically removable, except Type 1620 (BGA), which offers a ball grid array chip package and it typically mounted on the main system board.

Dimensions

To view a visual representation of M.2 form factor dimensions, click here.

2.5-inch (U.2)

The 2.5-inch form factor is the most common deployment of an SSD, and is offered with PCIe (with NVMe), SAS or SATA interfaces.  It is typically used in desktops, servers and storage systems built around hard disk drives (HDD).  This form factor is commonly associated with the term U.2 and is sometimes referred to as the U.2 form factor.  U.2 is defined as compliance with the PCI Express SFF-8639 Module specification, and no longer typically references SAS or SATA SSDs.

Add-In Card (AIC)

An Add-in Card (AIC) is a solid-state device that utilizes a standard card form factor such as a PCIe card. The AIC would usually use an interface such as PCIe, or possibly a mezzanine card of a standard form type.  Given the larger physical size over an SSM, the AIC would typically have larger capacity and potentially higher performance.  In addition, the larger size allows for the potential to add computational function to the storage device. Because of the versatility of the form factor, the AIC is a form factor that likely will constantly evolve for solid-state storage.

Actual SSC dimensions may be less, dependent on design.

PCIe cards can also come in multiple widths. Such a configuration allows mating with adjacent motherboard connectors, enabling increased performance by supporting more than 16 PCIe lanes.