--- title: "NVMe Does Not Specify the SSD Bay: E1.S, E3.S and the Physical Package" description: "Leviathan Systems — Technical content Published 2026-10-20; updated 2026-10-20." canonical: "https://www.leviathansystems.co/articles/nvme-ssd-form-factor-edsff-thickness-interface" last-updated: "2026-10-20" --- # NVMe Does Not Specify the SSD Bay: E1.S, E3.S and the Physical Package Leviathan Systems — Technical content Published 2026-10-20; updated 2026-10-20. An NVMe label does not identify an SSD's physical package or establish a supported bay. Compare the exact drive and enclosure variant with the server supplier's supported configuration. E1.S includes enclosure variants of different thicknesses; E3.S and E3.S 2T also differ physically. Equal drive count, capacity and protocol can therefore describe different hardware purchases. A form-factor specification defines design possibilities; the actual product and complete server configuration establish which implementation is being offered. ## Read the protocol and the physical package separately A line offering four NVMe SSDs tells the buyer too little about the hardware that will arrive. NVM Express separates the storage protocol specifications from transport mappings, including NVMe over PCIe. That explains the communication context; it does not identify the enclosure surrounding the drive. M.2, the 2.5-inch drive family and EDSFF forms such as E1.S and E3.S describe physical implementations with their own mechanical and connector requirements. M.2 itself can support different interfaces. The 2.5-inch designation is a form-factor name, not a measured enclosure width. Neither term can replace the actual drive specification. Read a proposed SSD as a combination: its storage protocol and interface, its exact mechanical variant, and the complete system that supports that implementation. SNIA also discusses CXL devices in EDSFF packages, so an EDSFF shape alone does not even establish that a device is an NVMe SSD. The related CXL article addresses the memory-resource question; this article concerns purchasing SSDs for an identified server. References: [N1](https://nvmexpress.org/specification/nvme-over-pcie-transport-specification/), [S1](https://www.snia.org/node/14267), [K3](https://www.kioxia.com/content/dam/kioxia/shared/business/ssd/data-center-ssd/asset/KIOXIA_EDSFF_Intro_White_Paper.pdf) ## E1.S leaves an enclosure choice unresolved SNIA's SSD Form Factors resource, updated December 2024, lists an E1.S symmetric enclosure at 9.5 mm thick and asymmetric enclosures at 15 mm and 25 mm. Those three rows share a listed width of 33.75 mm and length of 118.75 mm. The changing dimension is thickness. The resource also lists thinner E1.S forms, so these are selected enclosure variants rather than an exhaustive family definition. KIOXIA's E1 page separately identifies the 9.5 mm symmetric enclosure and the 15 mm and 25 mm asymmetric heatsink variants. It presents different heatsink options as a balance between cooling and storage density. Its information is qualified as of October 2025. For a buyer, removing the thickness from the offer removes a consequential part of the supplied item. A supplier can retain the E1.S name while changing the enclosure. Whether that change is acceptable depends on the specified server configuration. A statement that the server supports E1.S still needs enough detail to connect the offered product to the supported enclosure and bay arrangement. References: [S1](https://www.snia.org/node/14267), [K1](https://www.kioxia.com/en-jp/business/ssd/solution/edsff/e1.html) ## E3.S and E3.S 2T retain different packages KIOXIA's E3 table lists E3.S at 7.5 mm thick and E3.S 2T at 16.8 mm. Both short variants have a listed width of 76 mm and length of 112.75 mm. Keep the 2T designation visible: common short length does not make the two packages identical. The page qualifies its information as of October 2025. The same page links separate specification scopes for E3 mechanical/electrical design, thermal characterization, the EDSFF connector and its PCIe pinout. A connector reference answers only part of the compatibility question. KIOXIA's September 2021 E3 white paper describes implementations in which designers can provide interchangeability through suitable bay mechanics and carriers. That is a platform design option. It is not evidence that a particular server already includes that arrangement. An offer describing E3 support needs to identify which variant the actual bay supports, not rely on the family's design flexibility. References: [K2](https://www.kioxia.com/en-jp/business/ssd/solution/edsff/e3.html), [K3](https://www.kioxia.com/content/dam/kioxia/shared/business/ssd/data-center-ssd/asset/KIOXIA_EDSFF_Intro_White_Paper.pdf) ## The enclosure participates in the cooling arrangement The enclosure and heatsink occupy physical space while providing surfaces through which the device can reject heat. Changing their geometry changes the package presented to the surrounding airflow. This is why a thermal option is also a mechanical purchase detail. A thicker package can provide a different cooling arrangement while consuming more of the available packaging space. It does not follow that every thicker SSD runs cooler, uses more power or performs faster. The actual drive, its workload and the surrounding system determine those outcomes. KIOXIA's E1 discussion supports the design trade-off, not a result for an unspecified drive. Keep a form factor's allowable power envelope separate from the offered product's electrical and thermal requirements. A maximum-power column in a family overview is not the drive's actual consumption. Similarly, physical dimensions alone cannot establish the permitted airflow arrangement or supported drive population. Those questions require the system supplier's applicable configuration evidence. References: [K1](https://www.kioxia.com/en-jp/business/ssd/solution/edsff/e1.html), [K3](https://www.kioxia.com/content/dam/kioxia/shared/business/ssd/data-center-ssd/asset/KIOXIA_EDSFF_Intro_White_Paper.pdf) ## Four 8 TB drives can still be different purchases Consider two fictional offers for one identified server. The buyer's requirement stipulates a complete OEM-supported bill of materials using four 8 TB NVMe SSDs in the 9.5 mm E1.S enclosure, with its corresponding drive-bay, backplane and carrier arrangement. Offer A explicitly supplies that exact package. All offer details and support conditions are invented; this example represents no real product approval, installation or measured result. Offer B supplies four 8 TB NVMe SSDs but substitutes the 25 mm E1.S variant. It provides no corresponding supplier response identifying a supported drive-bay, backplane or carrier arrangement for the change. In both fictional offers, TB means 1,000,000,000,000 bytes, so four 8 TB drives total 32 TB of advertised raw capacity. Both say NVMe and E1.S. Those equalities preserve the component count, advertised capacity total and family labels. They do not preserve the supplied mechanical package. The 32 TB figure is not an application-available capacity claim. Under the stipulated requirement, A answers the purchasing question. B remains unresolved. The evidence does not establish B's compatibility, but it also does not justify declaring that every 25 mm E1.S drive is incompatible with that server family. The missing answer concerns this offered product and this configuration. If the supplier returns a supported complete arrangement for B, the buyer now has a different defined package to compare. Any changed drive-bay hardware, backplane, carriers or supported population belong in that comparison. Replacing only the capacity line would hide what the revised offer actually supplies. No fit conclusion can be calculated by adding drive thicknesses across a chassis opening. ## Compare the defined system before scoping physical installation Ask each supplier to identify the SSD model or part number, enclosure variant, exact server configuration, supported drive-bay/backplane arrangement and any required carrier, together with the OEM configuration reference or written support statement covering that combination. Resolve a substitution against that complete arrangement before treating the offers as equivalent. That decision is separate from the storage role. The B200 storage article distinguishes boot, local cache and external dataset storage. The GPU factory-configuration article distinguishes a complete supplied system from later product work. Those decisions still matter, but neither settles the SSD bay question. When the selected complete system also needs physical installation, Leviathan's GPU Infrastructure Physical Installation service and project inquiry are linked below. Share the exact supplied configuration, customer-furnished mounting and interconnect package, site and permitted physical tasks. The service covers agreed equipment mounting, physical IT connections, labels and installation records. SSD selection, internal product conversion and thermal qualification remain with their separately appointed owners. References: [L1](https://www.leviathansystems.co/services/gpu-assembly) ## Primary sources - [N1 — NVM Express: NVMe over PCIe Transport Specification overview](https://nvmexpress.org/specification/nvme-over-pcie-transport-specification/). Checked 2026-10-20. Explains the protocol/transport distinction. Used for terminology rather than product compatibility or a specific specification revision. - [S1 — SNIA: SSD Form Factors, updated December 2024](https://www.snia.org/node/14267). Checked 2026-10-20. E1.S dimension-table axes and physical-family/interface distinctions, including EDSFF use by CXL devices. - [K1 — KIOXIA: EDSFF E1 Form Factor](https://www.kioxia.com/en-jp/business/ssd/solution/edsff/e1.html). Checked 2026-10-20. October 2025 information on E1.S enclosure/heatsink variants and cooling-density trade-offs; use current product specifications for an actual offer. - [K2 — KIOXIA: EDSFF E3 Form Factor](https://www.kioxia.com/en-jp/business/ssd/solution/edsff/e3.html). Checked 2026-10-20. October 2025 dimension table and distinct mechanical, thermal, connector and pinout specification scopes. - [K3 — KIOXIA: Introducing the EDSFF E3 Family of Form Factors, September 2021 v1.2](https://www.kioxia.com/content/dam/kioxia/shared/business/ssd/data-center-ssd/asset/KIOXIA_EDSFF_Intro_White_Paper.pdf). Checked 2026-10-20. Historical design explanation of bay/carrier flexibility and the nominal 2.5-inch label; no market-availability forecast is adopted. - [L1 — Leviathan Systems: GPU Infrastructure Physical Installation](https://www.leviathansystems.co/services/gpu-assembly). Checked 2026-10-20. Project-defined mounting, physical IT connections, labels and records around customer-supplied equipment and permitted tasks. ## Related Leviathan resources - [B200 deployment storage: identify boot, cache and external storage roles](/articles/b200-deployment-guide) - [CXL memory expansion: separate host capacity from GPU HBM](/articles/cxl-host-memory-expansion-gpu-hbm-boundary) - [Configured GPU server or later GPU upgrade: compare the complete purchase](/articles/gpu-server-factory-configuration-versus-gpu-upgrade-kit) - [GPU Infrastructure Physical Installation](/services/gpu-assembly) - [Discuss physical installation for the selected complete system](/contact?service=gpu-assembly&from=/articles/nvme-ssd-form-factor-edsff-thickness-interface) ## Discuss physical installation around the selected system Share the exact complete configuration, site, customer-supplied mounting and IT connections, and permitted physical tasks to discuss scope and availability. [Discuss the scope](/contact?service=gpu-assembly&from=/articles/nvme-ssd-form-factor-edsff-thickness-interface)