Sprandom

Overview

Sprandom is a fast, pseudo-random preconditioning method for solid state drives, developed by SanDisk and presented at the 2025 OCP Global Summit. Rather than the slow conventional random-write process — which redistributes a drive's overprovisioning (OP) inefficiently only after garbage collection has begun — Sprandom short-circuits straight to the drive's target OP distribution in a single pass. It works by breaking the drive media into equal regions and creating a calculated amount of invalidity in each, using logical overlap that tapers over time plus a logical-address shuffle that eliminates the resulting locality artifact, so the outcome matches the OP distribution a true random write would produce.

Sprandom is exposed as a new FIO job type controlled by three parameters: sprandom=1 to enable it, the drive's actual physical overprovisioning, and num_regions (around 1000 is a good starting point for current-generation drives). It typically delivers 2-3x faster preconditioning depending on methodology and drive characteristics, with a best-case result of dropping random preconditioning from about 138 hours to roughly 7 hours on a 64TB drive. Sprandom produces the same steady-state performance numbers as conventional preconditioning — the drive snaps right to its target random-write performance — and the results have been replicated by two or three other companies. When tuning, the operator should watch for the point where high performance falls off to the target random-write performance; ideally that fall-off occurs shortly after Sprandom finishes, because the method should leave a little extra unconsumed OP.