How to check whether there is bad sector on an external USB hard disk on OS X?
How can I check whether there are any bad sectors on an externally connected USB hard disk drive?
Solution 1:
Related questions
- Fix bad blocks on Mac hard disk – includes some non-free and closed source software
- 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.
Essentially
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:
- GRC | SpinRite Data Recovery Technology (highlights)
Note the section about auto-relocation and the associated risk of dataloss.
SpinRite aside, fast forward a decade from 2003 to 2013:
- the unmistakable warning presented by Drive Genius 3 on a Mac.
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.
S.M.A.R.T.
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.
OS X SAT SMART Driver
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.
Solution 2:
The OS X built in command fsck_hfs has an option -S that apparently will check whether there is bad block on a USB hard disk on OS X.
From the official man page(Update: Bloody hell! Apple has removed the manpages from its site.):
-S Cause fsck_hfs to scan the entire device looking for I/O errors. It will attempt to map the blocks with errors to names, similar to the -B option.
Example:
fsck_hfs -fy -S /dev/disk3s11
It seems to be doing that when run on partitions without bad blocks but I've yet to check/document what it does when there are bad blocks.
Update: Warning: fsck_apfs cannot do this; while it also has a -S option, it does NOT cause a scan; it does something else entirely.