I read in many places that you should always do a "Verify Disk" in Disk Utility and resolve any errors before upgrading to Lion (currently running the last version of Snow Leopard on a MacBook Pro mid 2010).

I get the following error(s): "Incorrect number of thread records" and "Incorrect volume file count"


  1. What is the severity of these errors? Should I be concerned?

  2. I just finished "restoring" a USB thumb drive to a Mac OS Install DVD for Snow Leopard 10.6.3 (mid-2010). Note that the USB drive is equivalent to the install DVD and not an actual installed OS. As I understand it, it is possible to boot from my newly minted Mac OS Install USB to run the "Repair Disk" without entering the OS. (where I can fix my problem and go about my business).

Is my understanding correct? Does running the Repair Disk (from a USB, or in general) pose any risks? Is there anything else I should know?

I have a Time Machine backup going, if that makes any difference.


Using an installer image that is bootable, whether DVD or USB or simply an external partition, is always a good idea when repairing disc problems, because it allows the partition you need to check to be fully unused for the duration of the check. Otherwise it's trying to fix itself, whilst running the OS and the fix actions at the same time. So feel free to use whatever media you have to initiate a repair, the Disk Utility program is available in any OS X install media, just boot from it and select from the menu.

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