Where can I find information on how to create a hard drive data recovery application?

Question

Data recovery

OS - linux
File system - ext4
Programming language - C
1) display deleted files from disk;
2) create a disk image.
Where possible, look at some examples on this topic or read some material (English, Russian - it does not matter).
And one more less important, maybe stupid question, since I still don't understand the mechanics...
Let's say I manage to create a disk image, is it really possible to look for deleted data in the image?
Or do you need to restore what you can first, and then create an image?
If this is real, then the image will be the size of a hard drive?

Answer 1

Read the description of the format and source codes of a specific file system
What is the problem? Is the image different from the original disc?
Depends on the task.
If the hard drive is faulty, then it is better to merge everything from it into a disk image as soon as possible.
If the hard disk is normal, then it is possible (for the sake of saving space) to work with the original hard disk (read only, not write).
Yes, sure.
Image recovery uses another hard drive larger than the "recovery drive".
You can try to chew (compress) the image, but this is not guaranteed.

Answer 2

You need to learn the structure of ext4 - exactly how data (files, directories, overhead) is stored in the filesystem.
What are blocks, what are inodes.
And then you will be able to answer for yourself how easy it is to write a recovery program and in which cases it can help, and in which it cannot.