fdupes-4096byte-en.sh

# show version
fdupes --version

    fdupes 2.1.2

# Same size 10G file
ls -l

    合計 20971536
    -rw-r--r-- 1 root root 10737422336 2021/05/06_02:44:42 1.dat
    -rw-r--r-- 1 root root 10737422336 2021/05/06_02:47:10 2.dat

# Same for up to 4096 bytes
cmp *.dat

    1.dat 2.dat differ: char 4097, line 1

# clear disk chache
echo 3 > /proc/sys/vm/drop_caches

# exec

time fdupes .
                                        
    real    2m12.252s
    user    0m44.251s
    sys     0m12.606s

# Create a diff at byte 4096

    echo -n "a" | dd of=1.dat bs=1 seek=4095 conv=notrunc
    echo -n "b" | dd of=2.dat bs=1 seek=4095 conv=notrunc

cmp *.dat

    1.dat 2.dat differ: char 4096, line 1

# clear disk chache
echo 3 > /proc/sys/vm/drop_caches

# exec

time fdupes .

    real    0m0.224s
    user    0m0.004s
    sys     0m0.007s

# Fast because there is a difference within 4096 bytes