This is somewhat mitigated by the buffer cache. The random writes are stored in RAM and hit the disk later on, possibly when it would have been idle. On a developer laptop there is usually no difference. I remember I run some benchmarks with a pretty large test suite of a Rails application: POSTGRESQL in a ramdisk vs spinning disk: no difference in performance because the data never left the buffer cache. With substantial amount of data you hit the disk and solid state memory wins.