It may be 10% reserved to prolong SSD lifespan. Especially if they are using QLC memory (or as we should marketing-call it - 4-level MLC). Another idea - fully

It may be 10% reserved to prolong SSD lifespan. Especially if they are using QLC memory (or as we should marketing-call it - 4-level MLC). Another idea - fully populated SSD drive is slow, because when it has a lot of free space it can emulate SLC mode by using some space behind the scenes, freeing it when needed. Samsung calls this Turbo Write technology.