I dropped my external Seagate 2 TB hard drive on the floor. It seems to work fine. But I want to scan for bad sectors just to be safe. I use this drive for all of my TimeMachine backups.

The "macOS app for showing external HDD usage statistics?" post is about checking your hard drive and has tools you can buy (recommended by the community), or things you can try which I tried and which did not work.

On a Windows machine, you can take any connected drive, run scandisk on it, and detect/repair bad sectors. Is there a way to do this for my drive on Macintosh (without purchasing third party tools)?

More info:

  • Disk Utility -> Info says that SMART status is "unsupported".
  • The drive is formatted as HFS
  • In short - sending AT commands to the drive depends on the USB-SATA controller. If it's not supported, no software will be able to get the SMART status for you.
    – Allan
    Jun 6 '18 at 23:41
  • Here's the rub: most on here seem to agree with you. But I think I just found a way to solve this problem. Unfortunately, I can't post it as an answer to my own question because the community seems to have closed that by marking it a dupe and my edit does not seem to have fixed this. The answer was found in a post on OSX Daily. It turns out if you go to disk utility, click on "First Aid" - it will ask you if you want to "check the volume for errors and repair them if necessary". say yes, and after some time, you get a report. I think this might be the answer.
    – TMWP
    Jun 7 '18 at 18:29
  • In the linked dupe, I provide links to 2 tools that will do what you are looking for. That said, your entire question is about SMART status....
    – Allan
    Jun 7 '18 at 18:47
  • @Allan - respectfully - the question is really looking for how to take a HD like mine, on a Mac, without buying anything extra, and scan/fix bad sectors. My previous comment has the answer which I finally stumbled upon, but it would not make sense in the context of the "duplicate" pointed to. The "dupe's" answers, when tried - either did not work or required purchase of some tool. Is there some way I should further reword this question so I can post the answer to help others?
    – TMWP
    Jun 7 '18 at 19:25
  • I am going to try one more edit and then if the community still insists its a "dupe" I am going to let this go.
    – TMWP
    Jun 7 '18 at 19:31

In general you can't get SMART status of a drive in an external case. Some cases will support it, some do only with vendor-supplied software.

But SMART isn't all that useful. It's good at telling you the drive HAS a problem, not so good at telling you the drive might have a problem soon. And bad sectors on modern (21st century) drives are already mapped out by the drives controller - any sector that doesn't read reliably will just be mapped to a spare sector and you won't know about it.

Was the Seagate running when it was dropped? If no, no problem. They're designed to take some minor abuse when turned off. If yes, and you do manage to detect even a single bad sector then just replace the drive. Any bad sector that reaches user levels means the drive is out of spares, and that's probably because the head crash caused by the fall is now dragging a tiny bit of metal all over the platter.

In short, if you have any doubts about the reliability of spinning drives these days the most cost-effective route is to replace it. At $25-$60 per terabyte it just isn't worth the considerable time to verify the drive.

  • The drive was running when I dropped it. On my old windows 7 machine I could use scandisk to plug any bad sectors. I was hoping to do the same on my new Mac for this drive. As it is now in HSF Mac format, to do so would require a working Mac tool.
    – TMWP
    Jun 7 '18 at 2:22
  • Copy your data to a new drive and scrap this one. You have almost certainly caused a head crash, which means it will just get worse.
    – david
    Jun 17 '18 at 1:55

This article on osxdaily has a lot of good information that relates to this problem. The process that relates to this question:

  1. Use Mac Disk Utility
  2. In the UI, click First Aid
  3. You will be asked: "check the volume for errors and repair them if necessary"
  4. Yes - launches this process
  5. No - cancels the operation

A GUI window pops up that gives you a status as it runs multiple checks of your hard drive. In my case, the hard drive came up clean and the report then said nothing about sectors but did indicate my hard drive seemed in good working order. It gave details about many checks run, just no text about the sectors.

Someone else with a hard drive with bad sectors would need to try this to see what it does and what it says when a problem is found with a sector.

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