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How to tell whether I really have bad blocks on my boot drive?

A few days ago, while backing up my Mini's boot drive to an external using Carbon Copy Cloner, I encountered a bad read for a file that was suspected to be a bad block. The file was definitely corrupted, as I couldn't even copy and paste it and I had to replace it from a Time Capsule backup. Concerned, I obtained Drive Genius 3, and when I installed it Drive Pulse quickly noted two bad blocks on the boot drive.


I ran the included (with Drive Genius) Scan program with "spare blocks" selected, and it reported the two blocks and ran to completion. Then when I rebooted and ran Scan again just to make sure, it again reported two bad blocks.


This time I booted to the recovery disk and reformatted the drive while writing all zeros, as this is also supposed to tell the drive to stop using bad blocks. It ran to completion, I restored my backup from CCC, rebooted, and ran Drive Genius's Scan again. Again it reported two bad blocks.


How in the world am I supposed to lock these things out so I can again trust the drive? Is the drive just shot? I'm perplexed.


Thanks in advance!

MacBook Pro (17-inch Mid 2010), OS X Mountain Lion (10.8.1), Mac Mini Server; Time Capsule

Posted on Mar 12, 2013 2:39 AM

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Posted on Mar 12, 2013 4:27 AM

On modern hard drives, you should not have to ever think about bad blocks. Bad blocks are normally mapped out by the drive's firmware in the course of normal use. If you have persistent bad blocks that are not being mapped out, that may indicate that the drive itself is starting to fail.

3 replies

Mar 12, 2013 7:28 AM in response to thomas_r.

Thanks. Since this came to light exactly becuase data were on a bad sector, I'm thinking I should assume the drive is going south--especially given the massive effort I've already undertaken to try to lock out those sectors.


I still have over a year remaining on my Apple Care contract, guess it's time to poke them into replacing the drive.

Mar 12, 2013 12:11 PM in response to thomas_r.

Okay, spent about half an hour on the phone with Apple Enterprise tech support. Established a few things:


1. Drive Genius's boast about being used by at least some Genius Bar folks is true. There were two of them at the locaton of the tech I spoke with and they both verified that.


2. Drive Genius's Scan utility will report any bad blocks it encounters on the drive, not caring whether they've been mapped out by the OS.


3. There's an in-depth system diagnostic utility available at least to the Mac Mini Server, which is what I have. Power up holding Option-D and it seeks an internet connection and then loads the EFI version and runs system tests. I'm scrubbing the drive again just to be sure, said process expected to take 1-4 hours based on the user dialog.


It appears I'm worrying needlessly, which is always better than having something to be worried over.

How to tell whether I really have bad blocks on my boot drive?

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