How to check that a backup is really complete
A copy that says it finished is not proof. A bad cable, a full drive or a file in use can leave a damaged or missing file without any warning. The only proof is to compare each file with its original.
What a SHA-256 fingerprint is
SHA-256 turns the content of a file into a 64-character code. Change a single byte and the code is completely different. If the original and the copy have the same code, they are identical.
Compute it yourself
Windows (PowerShell): Get-FileHash file.pdf -Algorithm SHA256. macOS (Terminal): shasum -a 256 file.pdf. Linux: sha256sum file.pdf. Run it on the original and on the copy, then compare the two codes.
Good backup habits
- Keep at least two copies, on two different drives.
- Never let a backup tool delete files automatically on the source.
- Restore into a new folder, so that nothing is overwritten.
- Check the copy, not just the end of the copy.
The tool
Doing this by hand for thousands of files is not realistic. KDL Backup Care copies your folders, checks every file with SHA-256 and never changes or deletes the originals.