What is the Flash Translation Layer?
The Flash Translation Layer (FTL) in SSDs, told as a story about the garage's parts-warehouse manager, who links a catalog number to its real slot and always writes a change into a fresh one.
Asked to just swap slot 3 — but the whole box has to be cleared.Strange, right? A flash-memory warehouse can only clear whole boxes.
This warehouse clears only in whole boxes, and overused slots wear out.Clear and refill a slot too often, and it wears out for good.
FTL is the manager who links a catalog number to its real slot.The manager never overwrites the old slot — it writes into a fresh one.
The manager writes to a new slot, marks the old one, clears marked slots together, and spreads use evenly.Customers (the OS) never see any of this — they just look things up by catalog number (logical address).
The warehouse must keep spare empty slots, and it slows briefly while clearing old ones.FTL solves the no-overwrite problem, but spare space and brief slowdowns are the price.
The Flash Translation Layer (FTL) links a catalog number (logical address) to its real slot (physical address), and writes any change into a fresh slot instead of overwriting the old one.
The FTL is the layer inside an SSD that translates logical block addresses (LBAs) into physical NAND flash addresses. Flash can't be overwritten in place and can only be erased block-by-block, so a write marks the old page invalid and writes to a fresh page instead. Garbage collection later copies any still-valid pages elsewhere, then erases and reclaims blocks heavy with invalid pages, while wear leveling spreads writes evenly so no single block wears out faster than the rest.
When grown-ups say it
- Flash Translation Layer
- The warehouse manager linking a catalog number to its slot. Handles address translation, garbage collection, and wear leveling inside the SSD.
- Logical/Physical Address
- The catalog number vs. the slot's real number. FTL is what links the two together.
- Garbage Collection
- Gathering disposal slots and clearing them together. Writes can slow briefly while still-used slots get moved and the box is cleared.
- Wear Leveling
- Spreading use evenly across every slot. Prevents one slot from wearing out alone.
- Over-provisioning
- Slots kept empty in reserve, always. Protects both the SSD's write speed and lifespan.
- Block/Page
- The big slot that clears all at once, and the small slots inside it. Erasing works by block; writing works by page.
- Flash Memory
- The warehouse itself, which remembers parts even off power. FTL is the software that manages this very warehouse. → the parts warehouse that remembers even off power
- High Availability
- Holding up even when one slot fails. Covered in the SRE field, not this one. → when the spare generator takes over