write amplification
also: WA, write amp
Write amplification occurs when a single logical write operation to storage results in multiple physical writes to the underlying hardware, reducing effective write performance and lifespan of flash-based storage devices.
Write amplification is the ratio of actual data written to physical storage versus the logical data written by the application. For example, writing 1 MB of data might result in 5 MB of physical writes to the SSD, meaning a write amplification factor of 5.
This phenomenon is especially common in SSDs due to their internal architecture. SSDs erase data in large blocks (typically 256 KB–2 MB) but write in smaller pages (typically 4–16 KB). When updating existing data, the SSD must read the entire block, modify it in memory, erase the block, and write it back—causing significant overhead.
Write amplification matters because: (1) it reduces the effective lifespan of SSDs by increasing total writes beyond what the flash memory can endure, (2) it degrades performance as the drive works harder than necessary, and (3) it wastes I/O bandwidth. Modern SSDs use techniques like wear leveling, garbage collection optimization, and TRIM commands to minimize write amplification.