I've got an HFS+ formatted external drive that is starting to act a bit funny, mainly causing my mac mini (finder) to freeze up on occassion when accessing it.

Fearing imminent failure, what is the most comprehensive way to determine the health of the physical drive and the file system?

Verify in Disk Utility indicates the disk is fine, but weird behaviour would indicate otherwise.


Apple's Disk Utility doesn't have false positives but it can miss some errors.

Although it's not cheap Disk Warrior is magic for these sort of problems, in my experience it's fixed all non-physical-damage errors that I could throw at it.

If you're not keen to spend money, and if you've got the hard disk space, copying the contents off, repartitioning your external drive and copying back on on might clear up your problems. Copying the whole disk's contents (starting with what is most valuable to you, in case it dies while you're copying) is probably a good idea anyway, in case your disk is on its death bed.

  • Will Disk Warrior scan the disk to detect for errors first? I'm not even certain that the disk is defective..just trying to be preemptive – Josh Newman Dec 17 '10 at 22:29
  • Is it safe to Rebuild directories and/or Check Files/Folders even if the drive doesn't appear to have any issues? – Josh Newman Dec 18 '10 at 0:13
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    Yes on both counts - it's safe to run on a healthy drive. – glenstorey Dec 18 '10 at 1:46
  • Any experience with Drive Genius? – Josh Newman Dec 20 '10 at 3:21
  • Not me sorry! It looks more like a defrag than a disk checker. – glenstorey Dec 20 '10 at 6:29

Yes, Drive Genius allows to check surface for bad sectors even in demo mode:

Drive Genius screenshot

There is also option to perform an "Extended Scan" which checks disk for read and write ability of a disk (burn-in test for drives).

It also supports block remapping "Spare bad blocks" option but you should backup your data before doing this.

There is related question where some more utilities may appear in answers.

It's hard not to mention MHDD which gives much more information about what's going on with you disc while it scans it (instead of showing nice visualisation):

MHDD in work

Here is video from Youtube.

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    A "surface scan" is not a reliable way to diagnose a disk. It may be as ineffective as using S.M.A.R.T. analysis (which is probably the poorest way to isolate hardware faults). Additionally, block remapping should only be used immediately before you try and move the data from the drive, possibly preventing data corruption. Don't rely on it to restore your hardware to any reliable state. It is always best to download the utilities provided by the hardware manufacturers. They require windows, but since the drive is portable, shouldn't be a deal-breaker. – user10355 Apr 1 '12 at 19:26
  • You are absolutely right – Alex Bolotov Apr 1 '12 at 22:54
  • I ran the DriveGenius 4 demo tonight, and it would not let me run the "Physical Check" without buying a $99 license. The Extended check gave me an estimate of 41 days 16 hours to check a 2TB drive, but it was also unavailable in the demo. – datguy Jul 12 '16 at 4:18

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