Should I back up my backup now?

My external USB hard drive, which I use with Time Machine, isn’t recognised in Finder anymore. Disk Utility says that it can’t repair the disk and tells me to back it up and reformat it. But it is the backup drive! Is there any other software that might be able to rescue the drive? Duncan Swanlee Yes, but you don’t want them. Backup disks aren’t immune to the same random failures that can hit the internal storage in your Mac. Time Machine drives in particular receive about as much wear and tear as your main drive, because they are performing hourly backups whenever your Mac is in use. The hope is simply that both disks won’t fail at the same time. If your main drive fails before the backup, you replace it and restore from Time Machine. Likewise, if the backup drive fails first, you should simply replace that and create a new Time Machine backup. There are respectable third-party utilities such as DiskWarrior (www.alsoft.com) that can recover a hard drive, where Disk Utility cannot. You might be tempted by this option if your main drive fails and you don’t have an up-to-date backup, but it never makes sense for a backup drive. DiskWarrior costs $120 (about £80) and for that amount you could replace the backup drive. Backups are important enough that you don’t want to trust them to a drive that has failed once already. Remember: your data is always more valuable than the drive.