UK What E1.S means
E1.S is a solid-state drive form factor for servers and storage systems. The name stands for EDSFF 1U Short, where EDSFF is the Enterprise and Datacenter Standard Form Factor family. A group of server, cloud and SSD companies developed EDSFF to replace the 2.5-inch U.2 drive and the M.2 stick in data centres, and the specifications are now maintained by SNIA’s SFF Technical Work Group. E1.S itself is defined in SFF-TA-1006.
An E1.S drive is a narrow board, about 31.5 mm wide and 111.49 mm long, that stands on its edge in a front bay and plugs into a card-edge connector at the back. Every EDSFF drive speaks NVMe over PCI Express and uses the same connector family (SFF-TA-1002) and pinout, so servers and test equipment can share designs across sizes.
The point of the format is to fit more fast, serviceable flash into the front of a thin server than 2.5-inch bays allow, while giving each drive enough power and airflow to sustain PCIe 5.0 speeds.
E1.S thicknesses
All E1.S drives share the same width and length, but the specification allows several enclosure thicknesses. A thicker enclosure carries a larger heat sink, so it can draw more power and sustain higher performance, at the cost of fewer drives per server.
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5.9 mm. The bare board, typically up to around 12 W. Used where many drives sit close together, sometimes inside the chassis rather than in hot-swap bays.
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8 mm with heat spreader. A little more cooling, typically up to around 16 W.
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9.5 mm symmetric enclosure. Up to around 20 W and optionally eight PCIe lanes. A common choice for dense front bays.
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15 mm and 25 mm asymmetric heat sinks. Up to around 20–25 W per drive with less airflow needed. The 15 mm version is common in 1U and 2U servers that need full PCIe 5.0 performance.
EDSFF, U.2 and M.2 compared
E1.S sits in a family of related formats. The longer and wider members trade density for capacity and power, while U.2 and M.2 are the formats EDSFF set out to replace in servers.
| Form factor | Size (W × L) | Typical max power | PCIe lanes | Hot-swap | Typical use |
|---|---|---|---|---|---|
| E1.S | 31.5 × 111.49 mm | 12–25 W by thickness | x4, x8 option | Yes | 1U and 2U compute and GPU servers |
| E1.L | 38.4 × 318.75 mm | 25–40 W | x4 or x8 | Yes | High-capacity 1U storage arrays |
| E3.S | 76 × 112.75 mm | 25 W (1T), 40 W (2T) | x4 to x16 | Yes | 2U servers, U.2 replacement, CXL memory |
| E3.L | 76 × 142.2 mm | 40 W (1T), 70 W (2T) | x4 to x16 | Yes | High-capacity 2U storage |
| U.2 (2.5-inch) | 69.85 × 100.45 mm | Around 25 W | x4 | Yes | Existing 2.5-inch NVMe server bays |
| M.2 22110 | 22 × 110 mm | Around 8–9 W | x4 | No | Boot drives and compact systems |
Sizes are the published nominal dimensions. Power figures depend on the enclosure and the server’s cooling, so check the drive and server datasheets together.
Why GPU servers use E1.S
A GPU server has to feed several accelerators with training data, model weights and checkpoints, usually from the front of a chassis that is already crowded with fans. E1.S suits that job well.
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Density. Eight or more E1.S bays fit across the front of a 2U chassis, leaving room for air intakes.
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Speed. Each drive has its own PCIe 5.0 x4 link, so eight drives can deliver tens of gigabytes per second to the GPUs.
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Serviceability. Drives are hot-swappable from the front, with a latch and status LED, so a failed drive can be replaced without opening the server or stopping it.
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Cooling. Standard heat-sink options and a defined airflow path keep drives from throttling under sustained load, which is a weakness of M.2 drives buried on the motherboard.
E1.S vs U.2
U.2 is still the most common NVMe server bay, and many systems will use it for years. The SKY-641E3 GPU server, for example, has eight hot-swap U.2 NVMe bays. U.2 drives are thicker and offer high capacities in a familiar 2.5-inch caddy, and many models are available.
E1.S packs more drives into the same front panel, cools more predictably and is built from the start for PCIe 5.0 and beyond. The SKY-622G4 MGX GPU server uses eight front E1.S NVMe bays on PCIe 5.0, plus two M.2 slots for the operating system. Both formats are NVMe, so the software sees no difference. The choice is set by the chassis, so it is made when the server is chosen rather than later. Our rack mount servers include both types.
Quick answers on E1.S
These are the questions that come up most when E1.S appears on a server specification.
E1.S drives: common questions
What does E1.S stand for?
EDSFF 1U Short. EDSFF is the Enterprise and Datacenter Standard Form Factor family. The 1 means the drive fits vertically in a 1U chassis, and S means the short length, as opposed to E1.L, the long version.
Is E1.S NVMe?
Yes. Every EDSFF drive uses the NVMe protocol over PCI Express. There are no SATA or SAS E1.S drives.
Can an E1.S drive go in an M.2 slot?
Not directly. The connectors and sizes are different. Adapters exist for testing, but a server needs E1.S bays or an E1.S backplane to use the drives properly.
What is the difference between E1.S and E3.S?
Size and power. E3.S is a larger drive designed for 2U servers, with a higher power budget and up to 16 PCIe lanes. E1.S is smaller and suits 1U and dense 2U designs.
Is E1.S hot-swappable?
Yes. The format was designed for front-access hot-swap, with a latch and activity LED on each drive. The server’s backplane and operating system must also support hot-plug.
We fit E1.S, U.2 or M.2 NVMe drives in the servers we build as standard, sized to your data set and imaged with your operating system before the system ships.