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How can I check whether there are any bad sectors on a USB Hard Disk Drive?

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possible duplicate of Fix bad blocks on Mac hard disk – slhck Feb 27 '12 at 9:48
up vote 3 down vote accepted

Related questions

  1. Fix bad blocks on Mac hard disk – includes some non-free and closed source software
  2. What free or open source software can I use with Mac hardware to verify integrity of every block of a disk …?

It's sometimes inappropriate to use the automatic sector relocation capabilities of a drive, so the question raised by ohho becomes distinctive:

  • it's about discovery.


If there's a defective sector, then you'll either:

  • care about data within that sector; or
  • not care

– consider this before performing any action that may cause relocation (or remapping or sparing, or whatever you call it).

Why care?

Whilst SpinRite 6 is not for Macs, a 2003 page for version 5 is enlightening:

Note the section about auto-relocation and the associated risk of dataloss.

SpinRite aside, fast forward a decade from 2003 to 2013:

To the question here …

How to check whether there is bad sector on a USB harddisk on OS X?

For Mac – for OS X – I don't know of anything as capable and careful as SpinRite (nothing to disable auto-relocation).

So, as things stand: to verify the sectors of a disk on USB with OS X, we're probably limited to using utilities that may cause relocation. I can't estimate the degree of risk of associated dataloss, but if that risk is acceptable then I should steer first towards:

  • the utilities that are up-voted or recommended in related questions (1) and (2) above.

Hint: what's under related question (1) is more immediately user-friendly.


The OS alone can not use S.M.A.R.T. technologies on drives that are external on buses such as USB 2.0 and FireWire.

Elsewhere there's a wealth of information ( and misunderstanding ;) so I'll focus this part of the answer on just one point:

  • getting Apple's OS to work with S.M.A.R.T. technology with external USB and FireWire drives.


kasbert / OS-X-SAT-SMART-Driver on GitHub:

… a kernel driver for Mac OS X external USB or FireWire drives. It extends the standard driver behaviour by providing access to drive SMART data. The interface to SMART data is same as with ATA family driver, so most existing applications should work. The driver requires a SAT (SCSI ATA Translation) capable external drive enclosure. …

If you try this KEXT with Lion then – as with any third party kernel extension – proceed with caution.

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Only way to really know is to write to each sector and read it back to see if you get the same thing back, checking for errors on the way.

badblocks under Linux does this. badblocks has a nondestructive read/write test mode.

Under Windows, I believe if you invoke chkdsk with the /F, /B, and /R options it will test each sector for bad sectors. It is also non-destructive but I'm not sure if it actually writes to each sector to test.

This Superuser answer suggests that SpinRite 6 may also do the same thing but I haven't tested.

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Depending on the filesystem on the drive you could run

fsck_msdos /dev/disk1s1

This would check an FAT FS. Maybe that's what you want? Possible commands are:

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These commands check (and optionally repair) the volume data structures, they don't scan the disk for readability/writability of the disk surface. – Gordon Davisson Feb 27 '12 at 15:48

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