I have found issue with ext4 partition.
I created many many empty files with the following way:
[cy6ergn0m@cgmachine heap]$ seq 1 10000000 | xargs touch

But this command crashes asfter a while with a error 'no space left on
device'. At the same time, df -h shows that I have 7Gb free on this file
system. So, I can't create any file in any directory at this filesystem.

[cy6ergn0m@cgmachine heap]$ pwd
/e4/sandbox/heap
[cy6ergn0m@cgmachine heap]$ ls -1 | wc -l
1261144
[cy6ergn0m@cgmachine heap]$ df -h /e4
Файловая система      Разм  Исп  Дост  Исп% смонтирована на
(filesystem/size/used/available/used%/mounted)
/dev/sda4              28G  7.2G   19G  28% /e4
[cy6ergn0m@cgmachine heap]$ touch ttt
touch: невозможно выполнить touch для `ttt': На устройстве кончилось место
(touch: failed to execute touch for 'ttt': No space left on device)