I know that the purpose of overprovisioning is to give the SSD free space to move blocks to when writes occur, and to give garbage collection some space to play with. But how does the SSD know that an unpartitioned area is unpartitioned? And what if I suddenly decide to partition it? Will it damage any data being held in that unpartitioned space?

Partly what prompted me to ask this is the warning in the Samsung Magician software that "Using a RAW partition may damage your data."


AFAIK the way this is supposed to work is that the drive keeps track of which sectors are "free". Now, it doesn't know what kind of file-system you're using on it, so its notion of "free" is different from the file-system's. Basically, all it knows is that all sectors are "free" at the beginning of the drive's life-time, that sectors aren't free after they've been written to, and and later on the OS can tell the drive that some sector is "free" again using the all-too-famous TRIM command.

So the overprovisioning works by trying to make sure that the unpartitioned area is never written to, so those sectors stay as "free".

If you suddenly decide to use that area (i.e. write to it), then those sectors won't be "free" any more and you'll lose the supposed benefit of overprovisioning (at least until your OS decides that this area is free again and that the drive should be told about it via TRIM, which may very well be "never").

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