Fsck -- reports success in under 1 second on ~1 TB partition!

Linux
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1

Yesterday, fsck reported finding no errors on a ~ 1 TB partition in under a second!

The method used is provided below. I doubt fsck really did anything meaningful. So what mistake have I made in adapting the method described at Linux: Run fsck on LUKS (dm-crypt) Based LVM Physical Volume?

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[Boot from Live Ubuntu 16.04 USB]

ubuntu@ubuntu:~$ sudo fdisk -l

[...]

Disk /dev/nvme0n1: 953.9 GiB, 1024209543168 bytes, 2000409264 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: gpt
Disk identifier: C5CE78D6-06C1-4528-BF0F-098BAEE04CC0

Device           Start        End    Sectors   Size Type
/dev/nvme0n1p1    2048    1050623    1048576   512M EFI System
/dev/nvme0n1p2 1050624    2050047     999424   488M Linux filesystem
/dev/nvme0n1p3 2050048 2000408575 1998358528 952.9G Linux filesystem

[...]

ubuntu@ubuntu:~$ sudo  cryptsetup luksOpen /dev/nvme0n1p3 n1p3
Enter passphrase for /dev/nvme0n1p3:
ubuntu@ubuntu:~$ ls /dev/mapper/
control  n1p3  ubuntu--vg-root  ubuntu--vg-swap_1
ubuntu@ubuntu:~$ sudo vgscan
  Reading all physical volumes.  This may take a while...
  Found volume group "ubuntu-vg" using metadata type lvm2
ubuntu@ubuntu:~$ sudo lvs
  LV     VG        Attr       LSize   Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert
  root   ubuntu-vg -wi-a----- 867.47g
  swap_1 ubuntu-vg -wi-a-----  63.85g
ubuntu@ubuntu:~$ sudo vgchange -ay ubuntu-vg
  2 logical volume(s) in volume group "ubuntu-vg" now active
ubuntu@ubuntu:~$ sudo vgscan
  Reading all physical volumes.  This may take a while...
  Found volume group "ubuntu-vg" using metadata type lvm2

ubuntu@ubuntu:~$ sudo fsck -N -r -V  /dev/ubuntu-vg/root  -d -t -t -v
fsck from util-linux 2.27.1
[/sbin/fsck.ext4 (1) -- /dev/mapper/ubuntu--vg-root] fsck.ext4 -d -v /dev/mapper/ubuntu--vg-root

ubuntu@ubuntu:~$ sudo fsck  -r -V  /dev/ubuntu-vg/root  -d -t -t -v
fsck from util-linux 2.27.1
[/sbin/fsck.ext4 (1) -- /dev/mapper/ubuntu--vg-root] fsck.ext4 -d -v /dev/mapper/ubuntu--vg-root
e2fsck 1.42.13 (17-May-2015)
/dev/mapper/ubuntu--vg-root: clean, 1446440/56852480 files, 109170683/227401728 blocks
/dev/mapper/ubuntu--vg-root: status 0, rss 3404, real 0.121389, user 0.110465, sys 0.003945

ubuntu@ubuntu:~$ sudo fsck   /dev/ubuntu-vg/root
fsck from util-linux 2.27.1
e2fsck 1.42.13 (17-May-2015)
/dev/mapper/ubuntu--vg-root: clean, 1446440/56852480 files, 109170683/227401728 blocks

ubuntu@ubuntu:~$ sudo fsck  -r -V  /dev/mapper/ubuntu--vg-root  -d -t -t -v
fsck from util-linux 2.27.1
[/sbin/fsck.ext4 (1) -- /dev/mapper/ubuntu--vg-root] fsck.ext4 -d -v /dev/mapper/ubuntu--vg-root
e2fsck 1.42.13 (17-May-2015)
/dev/mapper/ubuntu--vg-root: clean, 1446440/56852480 files, 109170683/227401728 blocks
/dev/mapper/ubuntu--vg-root: status 0, rss 3096, real 0.127837, user 0.112030, sys 0.004001
  
 .

So where’s the mistake in running fsck?

Thanks,

2

Clean means there is nothing wrong with it. So fsck will not do full scan.

3

The reason for doing this scan is that once during boot the following showed up and nothing happened after that:

incomplete_fsck
incomplete_fsck3756×2112 1.84 MB

Other attempts to boot just end with the word “ubuntu” in the center of the screen with dots below the word.

So I have been trying to run fsck externally.

How does fsck know the partition is clean without scanning it fully?

I can understand fsck finishing in under a second if there were no files in the partition. But the files in the ~1 TB partition take up about 503 GBytes – fsck really check all of that in under a second?