What is qemu-img consistency check?

Question

I would be glad if someone could explain the meaning of qemu-img check <filename> command. Man pages provide very poor information about it:

   check [-f fmt] [-r [leaks | all]] filename
       Perform a consistency check on the disk image filename.
       If "-r" is specified, qemu-img tries to repair any inconsistencies
       found during the check. "-r leaks" repairs only cluster leaks,
       whereas "-r all" fixes all kinds of errors, with a higher risk of
       choosing the wrong fix or hiding corruption that has already
       occurred.
       Only the formats "qcow2", "qed" and "vdi" support consistency
       checks.

For instance, can I use this command in case of need to check the hash sum of the disk image (rather hash sums of the files stored on them)?

Solution

It is like a check disk on a physical file that constitute your virtual disk.

See the part: Only the formats "qcow2", "qed" and "vdi"

This mean that your virtual disk can be corrupted, wrong byte or missing data somewhere etc. Those formats seem to support some kind of checking and error correction, and that's the purpose of the option qemu-img check

Wiki for qccow2 shows consistency features for example