[jbotz]

> the same fixed length 16 byte file in the same location

On the SSDs you weren't writing to the same location. The firmware keeps mapping your writes to different locations for wear leveling. So if those 16 bytes are the only thing you're writing your SSD would last a very long time indeed!

> I had assumed the file system layer would take care of that kind of management for me

Depends on the file system; some do, some don't, and for some uses cases that isn't what you would want, so you need to chose your filesystem (or its options) appropriately. A journaling file system (like ext4 with -j) would never write to the same spot (but without -j it would), and a more advanced one with COW like btrfs usually won't either (but COW can be turned off).