Probably lucky. File names are md5 of the content, i am not sure if it helped on collision on 32 bit md4. The linked post mentions dir_index default and tune2f

Probably lucky. File names are md5 of the content, i am not sure if it helped on collision on 32 bit md4. The linked post mentions dir_index default and tune2fs -l lists the dir_index under Filesystem features only. Not knowing this default behavior, i was considering enabling dir_index explicitly to aid chocking rsync. EDIT: I ran the reproduction code with 200K instead of 100K just to be sure. There was no problem creating file as well as copying all the files to a different folder. The disk was formatted about 3 months ago and mounted with default options "ext4 noatime,barrier=0 0 0" . On original as well as copied folder `ls | wc -l` still gives 200000.