Most home users, and I dare say some system administrators, lack a backup policy. Their family pictures, music collections, and customer data files live on their hard drives and are never backed up to offline storage, only to be lost when the hard drive eventually crashes. A few users know to keep backups and regularly copy their files over to a safe storage medium. But even these conscientious people may find their strategy lacking when the time comes to recover from a system crash and they discover corrupted backup data. A successful backup strategy must involve checking for corrupted data.

Silent Data Corruption

The small number of users who keep copies of their important files only keep a single backup. Often, they use an external storage system, such as Tarsnap or a Nextcloud instance, periodically or continuously synchronizing the important files on their computers with the cloud. While a comfortable approach for end users, a single backup suffers a number of problems. Most importantly, single backups are vulnerable to silent data corruption.

Take for example a folder called Foals, which is full of pictures of happy young horses. My backup strategy consists of weekly copying the entire folder over to USB mass storage with a tool such as rsync [1]:

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