Mostly a matter of software not being written to make use of the SSD capabilities. You need parallelism or prefetching to keep the IO queues non-empty. If you h

Mostly a matter of software not being written to make use of the SSD capabilities. You need parallelism or prefetching to keep the IO queues non-empty. If you have a single-threaded workload which interleaves blocking IO with CPU work and the IO patterns are not amenable to readaheads the SSD will be mostly idle. Similarly anything calling fsync or performing other file system operations that trigger synchronous writes on the critical path will stall the entire boot process. Due to caching writes are fast no matter the medium as long as you don't demand instant durability.