When trying to edit a partition on my hard drive, Disk Utility says:

Couldn't modify partition map because the file system verification failed.

So I booted into single-user mode and typed in:

/sbin/fsck -fy

My computer then said:

The volume Macintosh HD appears to be OK.

I boot back up and check with Disk Utility, but when I select the particular partition, it wont let me edit it in Disk Utility and have it verified. It tells me to repair it. I try to repair but Disk Utility can't repair this disk, and it needs to be reformatted. How would I go about doing this?

  • Turns out you can reformat a single partition by using the erase functionality in disk utility
    – user55685
    Aug 24, 2013 at 1:47
  • user55685, please post your findings as an answer for other "Googlers" to see. Aug 24, 2013 at 2:14

1 Answer 1


To format a disk in OS X:

  1. Open Disk Utility.
  2. You can format either at the partition-level, or disk-level. If you have multiple partitions on a disk, you can erase just one or more than one. If you want to start over and re-partition the disc, you can do that without erasing it first.
  3. Once you have selected the disk or partition to format, click the Erase tab.
  4. Choose the type of disk format you want (generally you can stick with the default, `Mac OS Extended (Journaled)').
  5. Enter a name for the formatted disk/partition.
  6. Click Erase.

To re-partition without erasing first:

  1. Select the physical disk in the left-hand column. That is, the icon aligned to the left side of the window. Those indented are partitions on the physical disk. To re-partition you must have the physical disk selected.

    enter image description here

  2. Click the Partition tab.

  3. Select a Partition Layout from the drop-down menu.
  4. Give each partition a name.
  5. Click the Apply button.

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