Important data has to be backed up in professional environments and even at home where you have important photos, videos, documents, eMail etc which you don't want to loose. There exist a lot of tools on Linux (rsync, rsnapshot ...) to create backups. From time to time you should check whether the backup is identical with the original. It's uggly if you detect the backup is not complete when you actually need the backup.
Following tools exist to compare directories and to find missing directories and files:
diff -rq original/ backup/
rsync -rvnc --delete . backup # Without -c ony timestamps and filesizes are compared - no filecontents (much faster). --modify-window=1 should be used with FAT or NTFS filesystems
cd original hashdeep -rlc md5 * > ~/checksums.txt
cd backup hashdeep -ravvl -k ~/checksums.txt *