On Wed, Feb 13, 2019 at 01:14:36PM -0800, David Christensen wrote:
AFAIK over-provisioning has no effect on longevity -- longevity is proportional to total number of cells times rated erase/ write cycles per cell divided by write throughput.
In the absence of trim, restricting the logical capacity of the drive ensures a larger pool of cells known to the drive to be unused and available for wear leveling. Otherwise, if you write to a cell the drive has to always preserve the data in that cell even if you later erase the file you wrote there (because the drive doesn't know it was erased). This is essentially what the drive manufacturers do: they build a drive with capacity N but sell it as N-S where S is the amount of spare capacity held in reserve for wear leveling and to allow for cells to be removed from service as they reach end of life. In general, the more expensive the drive, the more it is overprovisioned to increase the longevity of the device.
On modern SSDs in light duty the difference is probably negligeable, especially if you occasionally fstrim to communicate how much of the drive is actually unused.
