after fs crash and running fsck, some files were recovered but not place in lost+found?

I had a I/O error on an external hard drive partition sdb4 (its usual mountpoint being /run/media/yan/data). The partition was non responsive, couldn't be accessed and refused to unmount. I did not know what to do but unplug the disk and replug it. After that I had error on its fs, so I ran fsck: sudo e2fsck /dev/sdb4 -y -v It was asking for a lot of fixes (thousands) but since data is non-critical on that disk, I ran it with -y. data contains a file system with errors, check forced. Pass 1: Checking inodes, blocks, and sizes Pass 2: Checking directory structure # Fixed invalid inode numbers, incorrect filetypes, cleared links, deleted/unused inodes Pass 3: Checking directory connectivity # Connected unconnected directory inodes to /lost+found Pass 4: Checking reference counts #Fix inodes ref count, connected unattached inode to /lost+found Pass 5: Checking group summary information # Fix block bitmap differences, blocks count wrong for group # Fix inode bitmap differences, directories count wrong for group, free inodes count wrong for group data: ***** FILE SYSTEM WAS MODIFIED ***** 72955 inodes used (0.14%, out of 51200000) 2390 non-contiguous files (3.3%) 17 non-contiguous directories (0.0%) # of inodes with ind/dind/tind blocks: 0/0/0 Extent depth histogram: 72264/636/1 186984621 blocks used (91.30%, out of 204800000) 0 bad blocks 34 large files 70447 regular files 2453 directories 0 character device files 0 block device files 0 fifos 4294966642 links 46 symbolic links (46 fast symbolic links) 0 sockets ------------ 71063 files So if I understand correctly, fsck managed to salvage 70k files, so most of the files since I had like 75-80k files on that disk. The problem is that only 20k files appear in '/run/media/yan/data/lost+found', and only 24k on the entire partition. [yan@machine ~]$ find /run/media/yan/data/lost+found | wc -l 19786 [yan@machine ~]$ find /run/media/yan/data | wc -l 23691 I reran fsck but he tells me that the partition is clear (and has 74k files ?) [yan@machine ~]$ sudo fsck /dev/sdb4 fsck from util-linux 2.28 e2fsck 1.42.13 (17-May-2015) data: clean, 74200/51200000 files, 186685980/204800000 blocks[/cpp] I also have very different disk usage according to df and du (I know there should be a difference, but here it seems too big to be normal): [yan@machine ~]$ df -h /run/media/yan/data Filesystem Size Used Avail Use% Mounted on /dev/sdb4 769G 700G 31G 96% /run/media/yan/data [yan@machine ~]$ du -sh /run/media/yan/data 586G /run/media/yan/data I'm guessing there is still recovered data that I can't access. My questions are : 1) Is it possible for recovered files by fsck to not be place in lost+found ? In that case, where are they ? 2) Is there any way to get back those missing files ? 3) If not, how do I free this space ? EDIT: I tried a more recent version of e2fsck on sourcejedi's recommandation: [yan@machine build]$ sudo ./e2fsck/e2fsck -f /dev/sdb4 e2fsck 1.43.3 (04-Sep-2016) Pass 1: Checking inodes, blocks, and sizes Inode 40501578 extent tree (at level 2) could be narrower. Fix? yes Pass 1E: Optimizing extent trees Pass 2: Checking directory structure Pass 3: Checking directory connectivity Pass 4: Checking reference counts Pass 5: Checking group summary information data: ***** FILE SYSTEM WAS MODIFIED ***** data: 74200/51200000 files (3.2% non-contiguous), 186685964/204800000 blocks It did not do much, lost+found still has the same file count and size.