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long story I have an USB drive to copy data between Mac, Windows (personally I don't own any) and PS4 - it is exfat formatted. Recently I noticed my Mac would freeze when I plug in this disc - also there is a directory in the top hierarchy that I could not open. Since this drive moves around a lot I suspected an unlucky disconnection caused corruption. Checked the drive and the only partition with disk-utility "first aid" - which report everything is fine. Despite this in the system log there are plenty of I/O errors. Looks like I need to trash it. But I sure had loved it if my mac gave me any warning that I was using a bad drive (I kinda forgive the PS4 that she didn't warn).

So for the future what check should I use?

I see that there are older questions discussing a similar questions, though they are 5 years old and also some of the link tools are dead now. Also this question is not about data recovery, but how to asses a drive.

tl;dr What program (on mac) can I trust to check my discs?

  • You might want to consider purchasing an external SSD for the inevitable replacement drive instead of spinning platters, which are so 20th century. – IconDaemon May 8 '17 at 11:51
  • If you have I/O errors for that drive in the system.log then you already have your answer, the drive is defective. Replace it! Disk Utility does not perform a full disk low level sector-by-sector test and that's why it can say a disk is okay when in fact it's not. You can use dd, which is already installed, to preform a low level sector-by-sector test. – user3439894 May 8 '17 at 12:39
  • @user3439894 I totally agree. My confusion is just - Finder won't alert me, diskutil tells me all is ok. In the future - how can I find out I am working on a "dying" disk? Hoping messages in system log will pop up doesn't sound reliable to me. Other OSes at least give some error message. – bdecaf May 8 '17 at 13:30
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I reccomend Disk Drill. Their diagnostic and monitoring tools are free, but the recovery is what (if you need it) you will have to purchase.

There's also a very robust set of command line (CLI) tools available as open source: smartmontools. This is a available as a macOS package so you don't need to install via brew or MacPorts.

Important: One thing to keep in mind when diagnosing external drives is that you have two components:

  • the drive itself
  • the USB enclosure

I have had USB enclosure's fail (the USB to SATA portion) that looked like a drive failure. The best way to get around this is to remove the drive (if you can) and use a separate USB-SATA Adapter. What you are doing is eliminating one of the components from the diagnostic equation (the USB interface) with a "known working" component. They are cheap (approx $10) to keep for diagnostic purposes.

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That said, a drive diagnostic is not a "quick status check." To find bad blocks you may need to do a "deep scan" because a bad block isn't report until the drive encounters a bad block.

  • I just tested Disk Drill - it seems only to look for deleted files. I couldn't see any indication of bad blocks or a bad drive. – bdecaf May 8 '17 at 12:10
  • I added some relevant info to the answer.. – Allan May 8 '17 at 12:26
  • Smartmontools looks promising. Took me some time till I found the kernel driver. And now it will run overnight with a selftest. – bdecaf May 8 '17 at 13:22

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