Comment by userbinator

On the other hand, your worst fragmented case still gets ~200MB/s with a random read, which is around the best case with a sequential read for most HDDs today. A 4k random read on a HDD will be 1-2MB/s at most.

Relatively speaking the SSD slows down to ~50% of its max speed with fragmentation, but the HDD will be down to around 1%. So fragmentation affects SSDs somewhat, but HDDs are affected much more severely.

(Which SSD was it, and how was the test setup? That's important for comparison purposes, as the layout of the filesystem blocks and how they correspond to the NAND eraseblocks/pages has a huge effect on what fragmentation will do.)