Sprandom: A Fast, Pseudo-Random Preconditioning Method for High-Capacity Solid State Drives

At the 2025 OCP Global Summit, SanDisk engineer Steven Sprouse introduced Sprandom, a fast pseudo-random preconditioning method for high-capacity SSDs. As drives scale to 64TB, 128TB and beyond, conventional random-write preconditioning can take days or weeks; Sprandom short-circuits straight to the target overprovisioning distribution in a single pass by writing equal media regions with tapering logical overlap and a logical-address shuffle. SanDisk integrated Sprandom into FIO version 3.41 (merged end of August 2025) and released it as open source, reporting typical 2-3x speedups and a best case of dropping random preconditioning from ~138 hours to ~7 hours on a 64TB drive.

Key Takeaways

• Random-write preconditioning that took 30-45 minutes on ~1TB drives now takes more than a day or weeks on drives beyond 64TB and 128TB, becoming a major bottleneck for development and qualification.
• Sprandom short-circuits straight to the target overprovisioning distribution in a single pass by creating calculated invalidity across equal media regions using tapering logical overlap plus a logical-address shuffle.
• Sprandom is a new FIO job type set with three parameters: sprandom=1, the drive's actual physical overprovisioning, and num_regions (~1000 for current-generation drives).
• SanDisk integrated Sprandom into FIO version 3.41, merged at the end of August 2025 and available in the latest open-source build.
• An OCP CL lab test on a 64TB drive cut random preconditioning from ~138 hours to ~7 hours; most users see 2-3x improvements, and results have been replicated by two or three other companies.
• Sprandom produces the same steady-state performance numbers as conventional preconditioning, with the drive snapping right to its target random-write performance.