File:File-Allocation-Visualization.gif

crude visualization of file allocation based on real data. 9MiB file testfile in a 64MiB ext4 filesystem overwritten 9 times (9x: dd if=/dev/urandom bs=1M count=9 of=testfile ; sync ; fibmap testfile).

yellow: free space red: currently known allocated sectors for testfile blue: free space (areas formerly belonged to "overwritten" testfile)