SYSTEM Cited by 1 source

E1.S form factor (EDSFF)¶

Definition¶

E1.S is an EDSFF (Enterprise & Datacenter Standard Form Factor) SSD variant — a thin, ruler-shaped enterprise flash module roughly equivalent in volume to a 2.5" U.2 drive but mounted edge-on, enabling denser front-accessible server packaging.

E1.S is Meta's current TLC flash deployment form factor. It was evaluated for QLC and rejected on volume grounds.

Why E1.S works for TLC¶

Dense front-access packaging.
Hot-swappable.
Adequate NAND-package count for typical TLC capacities.
Good thermal envelope for TLC write bandwidth.

Why E1.S doesn't scale to QLC¶

Meta's 2025-03-04 framing:

"While E1.S as a form factor has been great for our TLC deployments, it's not an ideal form factor to scale our QLC roadmap because its size limits the number of NAND packages per drive."

QLC's value proposition is density — packing substantially more bytes into the same drive slot. That requires more NAND packages per drive. E1.S's edge-on ruler volume imposes an upper bound on package count that is below Meta's QLC capacity targets (up to 512 TB standard, 600 TB with DFM). U.2-15mm wins on volume.

Two form factors, two tiers¶

A consequence of Meta's 2025 strategy: a single rack design can host both E1.S TLC drives (for high-BW / high-write / mixed workloads) and U.2-15mm QLC drives + DFMs (for read-dominant / batch-IO / capacity-dense workloads). Two form factors, two media tiers, one rack.

Seen in¶

sources/2025-03-04-meta-a-case-for-qlc-ssds-in-the-data-center — Meta's 2025 disclosure that E1.S is preserved for TLC while QLC moves to U.2-15mm.

systems/tlc-flash — the media tier E1.S hosts.
systems/u2-15mm-form-factor — the QLC-tier form factor E1.S couldn't scale to.
systems/qlc-flash.
companies/meta.