After a server crash a wanted to compare all actual files with the backuped data. An easy way is to compare the md5 hashes like that:
First create recursively md5 hashes from all files in that directory:
find ./backup -type f -print0 | xargs -0 md5sum > /checksums_backup.md5
Then check the actual data:
md5sum -c checksums_backup.md5
I was lucky, no files where damaged.