A reference of common enterprise/datacenter SSD form factors. Physical and electrical parameters (dimensions, power, PCIe speed, connector) come from published EDSFF/SNIA/NVMe specs and are reasonably solid. Board-level parameters (NAND package count, DRAM count, hold-up capacitor count) are not part of any form-factor spec — they're a per-vendor, per-model PCB design choice constrained by the available footprint, so these are left blank below to be filled in per drive.
U.2 (SFF-8639, "2.5-inch")
| Parameter |
Value |
| Dimensions |
69.85 mm x 100.45 mm (2.5" footprint); thickness 7 mm, 9.5 mm, or 15 mm |
| Cooling method |
Passive — chassis airflow across the metal case; no integrated heatsink |
| Max power |
~9-25 W typical (SFF-8639 defines multiple power classes; higher-power drives generally need the 15 mm case for surface area) |
| Max PCIe speed |
Up to PCIe Gen5 x4 (connector/spec headroom exists to Gen5+; most shipping drives are Gen4 x4) |
| # of NAND placements |
|
| # of DRAM |
|
| # of hold-up caps |
|
| Connector |
SFF-8639 (mechanically similar to SATA Express, repurposed pins for PCIe) |
| Protocols supported |
NVMe (PCIe), SAS, SATA — single-protocol per drive |
| Power rails |
3.3 V, 5 V, 12 V |
| Hot-plug |
Yes |
| Notes |
Legacy-dominant enterprise/datacenter form factor; being displaced by U.3 and EDSFF (E3.S) in new designs |
U.3 (SFF-TA-1001)
| Parameter |
Value |
| Dimensions |
Same as U.2: 69.85 mm x 100.45 mm, 7/9.5/15 mm thickness |
| Cooling method |
Passive — chassis airflow |
| Max power |
Similar envelope to U.2 (~9-25 W typical) |
| Max PCIe speed |
Up to PCIe Gen5 x4 |
| # of NAND placements |
|
| # of DRAM |
|
| # of hold-up caps |
|
| Connector |
Modified SFF-8639 with tri-mode pinout |
| Protocols supported |
Tri-mode: NVMe, SAS (up to 24G), or SATA — auto-negotiated in the same physical bay/backplane slot |
| Power rails |
3.3 V, 5 V, 12 V |
| Hot-plug |
Yes |
| Notes |
Mechanically compatible with U.2 bays; lets a backplane support NVMe/SAS/SATA drives interchangeably without redesign |
E1.S (EDSFF 1U Short, "gum stick")
| Parameter |
Value |
| Dimensions |
~118.75 mm length; width fixed to fit vertically in a 1U chassis; thickness variants: 5.9 mm, 8.0 mm, 9.5 mm, 15 mm, 25 mm |
| Cooling method |
5.9 mm/9.5 mm: passive/minimal, chassis airflow; 15 mm/25 mm: integrated heat spreader or heatsink |
| Max power |
~20 W (9.5 mm) up to ~25 W (15 mm, 25 mm) — varies by vendor |
| Max PCIe speed |
Up to PCIe Gen5, x4 standard, x8 optional on some variants |
| # of NAND placements |
|
| # of DRAM |
|
| # of hold-up caps |
|
| Connector |
EDSFF native connector (SFF-TA-1006) |
| Capacity range (typical) |
~800 GB - 8 TB |
| Hot-plug |
Yes |
| Notes |
Designed as the boot-drive/mainstream successor to M.2 in hyperscale 1U servers; up to 32 drives per 1U chassis in dense configs |
E1.L (EDSFF 1U Long, "ruler")
| Parameter |
Value |
| Dimensions |
~318.75 mm length; thickness variants: 9.5 mm, 18 mm |
| Cooling method |
9.5 mm: passive; 18 mm: heat spreader/heatsink for higher sustained power |
| Max power |
~25 W (9.5 mm), ~40 W (18 mm) |
| Max PCIe speed |
Up to PCIe Gen5, x4/x8 |
| # of NAND placements |
|
| # of DRAM |
|
| # of hold-up caps |
|
| Connector |
EDSFF native connector (SFF-TA-1006) |
| Capacity range (typical) |
Up to ~60 TB per drive; ~1 PB per 1U chassis achievable |
| Hot-plug |
Yes |
| Notes |
Maximizes capacity density per rack unit; primarily targeted at QLC-based, capacity-optimized (cold/warm tier) storage |
E2 (EDSFF 2U, emerging / not yet finalized)
| Parameter |
Value |
| Dimensions |
~200 mm (length) x 76 mm (height) x 9.5 mm (thickness) — sized to fit vertically in a 2U chassis |
| Cooling method |
Passive air cooling may not be sufficient at the top of its power range — proposal explicitly flags that liquid or other alternative cooling may be required |
| Max power |
Up to ~80 W (typical operation cited around 20-30 W) |
| Max PCIe speed |
PCIe Gen6 x4 (or better) targeted |
| # of NAND placements |
64 NAND package sites — this is one of the few form factors above where the spec itself targets a specific NAND package count, driven by the capacity goal below |
| # of DRAM |
|
| # of hold-up caps |
|
| Connector |
Builds on SFF-TA-1002 and SFF-TA-1009 (same connector family as E3) |
| Capacity range (typical) |
Up to ~1 PB per drive (QLC-based); up to ~40 drives (~40 PB) in a 2U node |
| Hot-plug |
Yes (expected, consistent with other EDSFF form factors) |
| Status |
Proposed, not yet a ratified/mature spec. SNIA SFF TA TWG opened this as a new project (with OCP/Micron involvement) in March 2025; first draft targeted 1-2 months after that. Treat all values here as directional/early — they're likely to shift before finalization. |
| Notes |
Positioned as a "warm tier" form factor — denser and cheaper per TB than E1.L, sitting between high-capacity SSDs and HDDs for AI/HPC/HCI datasets that need better-than-HDD access speed without full flash-tier cost |
E3.S (EDSFF 3" Short)
| Parameter |
Value |
| Dimensions |
76 mm (height) x 112.75 mm (length); thickness: 7.5 mm (1T) or 16.8 mm (2T) |
| Cooling method |
1T: passive, chassis airflow; 2T: heat spreader/heatsink for higher power |
| Max power |
1T: ~25 W; 2T: ~40 W |
| Max PCIe speed |
1T: PCIe Gen5 x4; 2T: PCIe Gen5/Gen6, x4/x8/x16 |
| # of NAND placements |
|
| # of DRAM |
|
| # of hold-up caps |
|
| Connector |
SFF-TA-1002 "Protocol Agnostic Multi-Lane High Speed Connector" |
| Capacity range (typical) |
Roadmapped toward 60+ TB |
| Hot-plug |
Yes |
| Notes |
Considered the intended long-term replacement for U.2/U.3 2.5" drives; better signal integrity than SFF-8639 at high PCIe speeds |
E3.L (EDSFF 3" Long)
| Parameter |
Value |
| Dimensions |
76 mm (height) x 142.2 mm (length); thickness: 7.5 mm (1T) or 16.8 mm (2T) |
| Cooling method |
1T: passive/heat spreader; 2T: heatsink, larger surface area for sustained higher power |
| Max power |
1T: ~40 W; 2T: ~70 W |
| Max PCIe speed |
PCIe Gen5 (Gen6 roadmapped), x4/x8/x16 |
| # of NAND placements |
|
| # of DRAM |
|
| # of hold-up caps |
|
| Connector |
SFF-TA-1002 |
| Capacity range (typical) |
Highest-capacity EDSFF option; targets both storage-dense and performance-dense (accelerator-capable) chassis |
| Hot-plug |
Yes |
| Notes |
Larger board area also positions E3.L as a candidate for GPU/accelerator/NIC modules, not just SSDs, in future E3-based chassis |
M.2 (2280 / 22110)
| Parameter |
Value |
| Dimensions |
22 mm width; common lengths 30/42/60/80/110 mm (enterprise drives typically use 22110 — 110 mm — for extra board space) |
| Cooling method |
Passive; typically none integrated, relies on motherboard/chassis heatsink or airflow — a common bottleneck at sustained enterprise loads |
| Max power |
~4-11 W typical (thermally constrained by the small, unshielded PCB) |
| Max PCIe speed |
PCIe Gen4 x4 common; Gen5 x4 emerging |
| # of NAND placements |
|
| # of DRAM |
|
| # of hold-up caps |
|
| Connector |
Edge connector, keyed (B, M, or B+M key) |
| Hot-plug |
No (typically socketed, not hot-swappable) |
| Notes |
Used in enterprise mainly for boot drives, cache/tiering drives, or edge/embedded servers — not primary bulk data storage, due to thermal and capacity limits vs. EDSFF/U.2 |
| Parameter |
Value |
| Dimensions |
Standard height 111.15 mm or low-profile 68.9 mm bracket; length up to ~312 mm (full-length), ~168 mm (half-length) common; single/dual/triple slot width |
| Cooling method |
Passive heatsink or active fan, sized to the card's power envelope; full-height cards allow the largest heatsinks of any form factor here |
| Max power |
Up to 300 W air-cooled (spec allows up to 600 W with adequate cooling), though SSD AICs are typically far lower (25-75 W) |
| Max PCIe speed |
Up to PCIe Gen5/Gen6, x1 to x16 (standard slot electrical/mechanical range) |
| # of NAND placements |
|
| # of DRAM |
|
| # of hold-up caps |
|
| Connector |
Standard PCIe edge (card) connector |
| Hot-plug |
Generally no (some enterprise implementations support surprise/managed hot-plug) |
| Notes |
Largest board area of any form factor here — used for very high-capacity or high-performance drives, or drives with on-board compute/FPGA/computational storage functions |
Notes on Blank Fields
NAND package count, DRAM package count, and hold-up capacitor count are not standardized by any of the form-factor specs above — they're determined per-drive by the vendor based on target capacity, DRAM-to-NAND ratio, and required power-loss-protection energy budget, all within the available PCB area for that form factor/thickness. These are best filled in from a specific drive's datasheet or teardown rather than the form-factor spec itself. As a rough intuition: thicker/longer form factors (E1.L, E3.L 2T, U.2 15mm, PCIe AIC) have more board area and generally allow more NAND packages and more hold-up capacitance than thin/short ones (M.2, E1.S 5.9mm).
Sources