SSD TBW

I found out that a common measure of the projected life of an SSD is
being given in units of “terabytes written” (TBW). This will typically
be much larger than the capacity of the drive itself, because it
includes the sum total of all write operations on the drive, including
deletion of data.

For example, a 1-terabyte drive could have an expected figure of
merit, by this measure, of 1000TBW -- that means it should be able to
endure a total of a petabyte (1000 terabytes) written to it before
showing signs of failure.

But it seems to me, a 2-terabyte drive made of parts with the same
quality, meaning each storage cell has the same expected endurance as
before, should have a proportionately greater figure of merit, namely
2000TBW.

But the bigger drive will likely not last longer than the smaller one
-- unless you don’t actually make use of the extra space.

So why not divide the TBW by the actual capacity of the drive? Then
you end up with a ratio of how much can be written in total, to the
drive capacity -- call it, say, the “cumulative write ratio”. Both
those drives would have a cumulative write ratio of 1000.

That number, it seems to me, correlates better to the overall quality
of the unit than TBW does. E.g. if you see a bigger drive with a
smaller cumulative write ratio, you can suspect that they are cutting
corners somewhere to keep the cost down.