Zombie curve is a way of characterizing GC overhead of a workload. A zombie curve shows the sorted valid ratios (# of valid pages in a block / # of pages in a block) of flash blocks with live data. Zombie curves and their animations clearly show a workload's pressure to an SSD's garbage collector. The above is an example of the animation, which compares the zombie curves of running SQLite-RollBack on ext4 and F2FS. The animation shows that the curves of both ext4 and F2FS enter a stable state, where the curve of F2FS indicates much more zombie blocks (i.e., blocks with some valid and some invalid data), which give lots of pressure to the SSD's garbage collector. The garbage collector has to frequently move data to free some blocks.