How to check archived backups?

Question

Backup

No wonder there is a saying that people are divided into those who do not make backups, who make backups and those who check backups. And how is it to “check backups”, if we are not talking about SQL databases that can be deployed and made sure that they work, but about a simple photo archive, for example?

There is a home Archive ~ 1TB.
I want to regularly make backups on two disks with my hands (to take one of them to work).
How to check if the backup was successful? How to make sure that half of the photos didn't lose pixels/bytes along the way?

Selectively check by hand? Or is there specialized software?
Or, for example, does Total Commander (or Acronis True Image) take care of the correctness of the backup when creating a backup? Or is there some other "checker"? Or are the tools mentioned enough?

Thanks in advance, I always choose Answer-solution.

Answer 1

Get MD5 from source files and compare with backup.

Answer 2

Or, for example, does Total Commander (or Acronis True Image) take care of the correctness of the backup when creating a backup?

No, verification takes time, if it were done automatically when copying each file, then copying would be slower, and no one wants this. Therefore, verification is a separate process, only if necessary.
I don’t know about Total, but its main competitor FAR can compare folders by the contents of files; maybe Total can do that too.
But this is a momentary decision, after the backup, check while the original is available. Verification may be required when the original is not at hand. For example, a working disk has died, there are two backups, but the contents of one file differ between these two backups; How do you know which one is correct and which is wrong? To do this, you can calculate checksums or hash sums of files. One of the most popular (to clarify: for everyday verification) hash algorithms is MD5. On Linux, the md5sum command out of the box is able to calculate all the files in a folder, as well as check against hashes previously written to a text file. On Windows, this is worse, it's easy to google a command to calculate the MD5 of a single file, but not all files in a folder. You have to install additional software, for example this one: www.nirsoft.net/utils/hash_my_files.htmlOr write your own script.
Count hashes from original files, write hashes to a text file, backup this text file along with everything else. When you need to check - count the hashes from backup files and check with those recorded in the file.

Answer 3

A known problem is to write a program that will check the correctness of the backup, but who will check the verifier? write another program?
There is a good chance that if there is an error in the code for organizing and checking the backup, that it will be the file list accounting code, i.e. if you make a mistake in specifying what to back up (for example, you forgot to add a new directory), then the check scripts using the same list of files and directories as the backup scripts will not detect this.
Therefore, ultimately, you need to do it manually, not trusting your early settings.
ps on the topic, for example, if you use the popular winrar archiver, then it has the option to check the archive after archiving, as well as any file comparison or hash calculation utilities, the same md5sum (linux utility package can be obtained by installing cygwin)