When I try and repair my external hard drives (I have two corrupt now some how both I think from improperly ejecting from the same machine), I get this message:

Disk Utility can’t repair this disk. Back up as many of your files as possible, ?reformat the disk, and restore your backed-up files.

Do I just have to reformat them now? Whats the next step? Both where being used as backups for the most part with a few files. Thank you for your time.

  • Please add the whole output of the Disk Utility check (if there is more than you have posted already)! It may indicate what's actually wrong. Additionaly check your log files with Console.app for errors (e.g. I/O errors) and add some example errors to your question if you find any.
    – klanomath
    Commented Jan 5, 2015 at 7:40

2 Answers 2


If your disks have non-critical data you can live without, and you just want to wipe them clean, use Disk Utility. If you're not in a rush use the Secure Erase/Zero Fill option as this will take any bad sectors out of use that may have formed since you acquired the drives.

Alternatively, if you have data you really need to access, try DiskWarrior as it can repair many disk issues that Disk Utility/FSCK can't.


If you have essential data on the drive and do not want to erase it you can usually copy all your data to another drive using FreeFileSync. It's free, extremely stable, and has a user friendly interface. It also gives you constant progress reports which is very reassuring.

I used this on a 2TB Time Machine drive that failed and could not be repaired with DiskWarrior and was hard to even mount. Owing to the damage to the drive it took a week to transfer about 800 GB comprised of 2.5 million files, slowing to a crawl or pausing for a couple of minutes. Normally it's extremely fast for making large copies.

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