[HarryT]

I back up all my important files (Calibre library, iTunes library, personal documents, etc) once a week onto an external USB drive using the very good (and free) Microsoft "SyncToy" tool. Today, when I ran the backup, it got half way through the scan in which it decides which files have changed, and hence need copying, and then failed with an error. Investigation revealed a seemingly irrecoverably corrupt file system on the external drive: presumably the result of a hardware failure, given that I'm scrupulous in correctly dismounting drives.

I'm now in the process of doing a sync to a new external drive to create a new backup.

Just goes to prove the old maxim, that there are two types of hard disk: those that have failed, and those which are about to fail!

I haven't lost any data, but it shows the importance of doing regular backups, and that backup drives themselves can (and do) fail.