Model

Write amplification of garbage collection

To free the block, you copy the v fraction elsewhere. Only (1 − v) of the block becomes new free space.

WAF = \frac{1}{1 - v}

$WAF$: Write amplification; bytes physically written to flash ÷ bytes the host asked to write
$v$: Valid fraction; the fraction of its pages that are still valid

How it behaves

One input on the horizontal axis, the others held fixed.

Data table

Every number the mechanisms quote for this relationship is recomputed from it, so none of them disagrees with it.

Each mechanism states it in its own names. The general symbol each name stands for is shown with it.

Physical Substrate & Performance Laws
Why do trade-offs exist at all?
$WAF = 1/ (1 - v)$
Read it in place →
Storage: Physical Organization
What should sit next to what, given that I must decide at write time and find out at read time?
$\frac{u}{1 - u} bytes moved per byte freed; 1 + \frac{u}{1 - u} = \frac{1}{1 - u}$
u (live fraction of the unit) = $v$
Read it in place →