Write Amplification Factor

Overview

Write Amplification Factor (WAF) is the ratio of data actually written to SSD media versus the data written by the host. At the 2025 OCP Global Summit FDP panel, speakers described WAF as having evolved from a theoretical proxy metric into a real problem — driven by QLC drives needing endurance and by GPU/AI workloads using storage as memory. They distinguished drive WAF (the interface-to-media ratio) from total WAF, which also includes application-level overhead such as RocksDB compaction and file-system metadata; measuring from the data entering RocksDB down to data written to media gives total WAF, while the drive interface-to-media ratio is drive WAF.

Reducing WAF reduces the energy the device uses, prolongs device life, and improves performance because internal device bandwidth is no longer wasted on garbage-collection housekeeping. FDP is the lever the panel used to push WAF toward 1.0: drive WAF was driven near 1.0 in RocksDB and Linux-kernel-build tests, and Solidigm's multiple reclaim group FDP cut a hyperscale workload's WAF from 3.06 to 1.01 in simulation.