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Why do I need to certify a SSD with 2 or more passes?
Some SSD controllers use data compression to minimize the amount of data written to flash memory. This reduces wear on the flash and can produce artificially high write speeds in benchmark tests — most benchmarking applications write blocks of zeros, which compress extremely well and do not reflect real-world performance.
While hardware compression is less common in modern NVMe drives than in earlier SSDs, SoftRAID’s certification process is designed to test all drives thoroughly regardless of controller type. Every pass except the last writes a non-compressible random data pattern, ensuring that as many memory locations as possible are genuinely tested rather than compressed away by the controller.
Why zeros alone are not enough
Writing zeros to an SSD is not sufficient to test it thoroughly. Modern controllers recognize zeros as highly compressible data and may not actually write to all physical flash cells — they can essentially map the zeros without performing real writes to every memory location. Some controllers may also trigger TRIM-like behavior when zeros are written, marking blocks as empty without writing to them at all.
Random data cannot be compressed or optimized, so SoftRAID’s Certify Disk command forces the controller to write to every cell. This is why SoftRAID writes random data on all passes except the last.
The final pass writes zeros, returning the drive to “as new” condition and ensuring it is ready for use.