Recover ext4 file system after quick format

Question

I accidentally formatted one of my drives and I'm hoping that I can recover a major part of my file system as I 'only' did a quick format.

After installing a second identical hard drive, I quick formatted the wrong drive by accident via Ubuntu's (14.04) Disks-Application. The drive was in ext4-format before and I did the quick format to ext4 again. There was only a single partition on the drive. Just a few seconds after the damage had been done, I unmounted the drive to avoid accidental writes.

The files I am after are in binary format (with no extensions as far as I am aware such as .npy .t7 .mat), some are .txt files.

Reading through forums and blogs, I understood that Testdisk+Photorec might be able help recover the lost partition. I gave Photorec a quick try but since most of the important files are binary and have no file signature I ended up having thousands of useless .txt files and non-readable .mat files. Testdisk on the other hand, displays inconclusive prompts as far as I understand. I did not yet attempt to perform a deep scan, as I expect the information to be at the very beginning of the drive (the drive is 8TB). See the following Testdisk snapshots for more info:

Partition selection screen

Advanced menu after selecting None as partition type

• Selecting EFI-GPT or Intel as partition type results in Testdisk telling me that there are no partitions available.

Analysis of the drive (after selecting None-type) results in the partition that is empty (except for an empty lost+found). In contrast, analyzing the drive after selecting the GPT-type results in many identical entries of this type: ext4 0 0 1 972801 80 63 156280533168

Superblocks:

superblock 0, blocksize=4096
superblock 32768, blocksize=4096
superblock 98304, blocksize=4096
superblock 163840, blocksize=4096
superblock 229376, blocksize=4096
superblock 294912, blocksize=4096
superblock 819200, blocksize=4096
superblock 884736, blocksize=4096
superblock 1605632, blocksize=4096
superblock 2654208, blocksize=4096

Questions

1. What does Ubuntu do specifically to the drive when selecting quick format? Can we infer from that whether it is (im)possible to recover the file system at all?

2. Can I recover parts of the structure using Superblocks? Somewhere I read that a backup superblock is written at position 1024. Is that recoverable or has that been cleared via quick format as well?

3. What options except file recoveries like Photorec or Scalpel remain for me to recover my file system? I know the full paths of some of the most important files I want to recover.

Answer 1

I was successfully able to recover all my files using a backup Superblock! After TestDisk was not able to help me, I tried an approach from a related question. For the sake of clarity, here the steps I took to recover my file structure:

1. Make sure your drive is unmounted.

2. Find out your backup Superblocks via

   dumpe2fs /dev/<drive-id> | grep -i superblock

   e.g. dumpe2fs /dev/sdb | grep -i superblock

3. Check the file system based on one of the Superblocks but do not apply any changes yet to see whether this particular Superblock is structurally intact.

   fsck.ext4 -v -n -C 0 -b <Superblock> /dev/<drive-id>

   e.g. fsck.ext4 -v -n -C 0 -b 2654208 /dev/sdb

   -v makes the command verbose to show more details, -n makes sure no attempts to fix the file system are made by always answering 'no' to each prompt, -C 0 displays a progress bar and -b defines the starting position of a Superblock given by the previous step.

4. If a suitable Superblock has been found, let fsck.ext4 fix your file system by replacing the -n with -y to accept all fixes automatically.

   fsck.ext4 -v -y -C 0 -b <Superblock> /dev/<drive-id>

5. Reboot and mount the drive.

In my case, the first level of directory names could not be recovered. Thus they could all be found based on their inode name in the lost+found directory, which is hidden.