SYSTEM Cited by 1 source
TLC flash¶
Definition¶
TLC (Triple-Level Cell) flash is a NAND flash variant that stores 3 bits per cell (8 voltage states). The dominant data-center flash tier as of 2025 — higher endurance + higher write bandwidth than QLC, lower density + higher cost-per-byte.
Position in the hierarchy¶
| Media | Bits/cell | Data-center role (Meta 2025) |
|---|---|---|
| SLC | 1 | niche, low-latency cache |
| MLC | 2 | legacy |
| TLC | 3 | primary flash tier |
| QLC | 4 | middle tier below TLC (new, 2025) |
Meta's TLC deployment¶
Meta's existing flash deployment is TLC in the E1.S form factor. The 2025 QLC post frames E1.S as "great for our TLC deployments" — the contrast implies TLC is continuing, not being replaced. QLC is a new tier below TLC; both coexist.
Why QLC doesn't replace TLC¶
- Write-heavy workloads still need TLC's better endurance and higher write throughput.
- Latency-sensitive mixed workloads where reads compete with writes benefit from TLC's smaller R/W asymmetry.
- Metadata / index / WAL paths (small, write-heavy, durable) need TLC.
QLC extends Meta's flash deployment downward on the BW/TB spectrum; TLC remains the tier for workloads above that band.
Seen in¶
- sources/2025-03-04-meta-a-case-for-qlc-ssds-in-the-data-center — framed as the incumbent tier QLC sits below in Meta's new three-tier (HDD / QLC / TLC) flash strategy.
Related¶
- systems/qlc-flash — the newer, denser tier QLC sits below.
- systems/e1s-form-factor — Meta's TLC form factor.
- concepts/bandwidth-per-terabyte / concepts/storage-media-tiering / concepts/write-endurance-nand.
- patterns/middle-tier-storage-media.
- companies/meta.