Disk Utility Erase Free Space vs. Data Rescue 3


macrumors newbie
Original poster
Apr 21, 2012
MacBook Pro "Core 2 Duo" 2.16 15 2006-7
OS X 10.6.8

I recently put some stuff in the trash and started to empty it, when I realized there shouldn't have been that many files in the trash and stopped it; but some stuff got zapped. After some research, I downloaded Data Rescue 3 onto an external drive, and ran it from there without installing. I had about 20 gigs of free space on the HD and I went ahead and recovered most of it to the external drive, to go through later when I have the time. I didn't lose anything really critical, and I have backups of most of it, so going through all those files can wait. But in the process of reviewing what was found in the empty space on my drive, I realized there was a lot of stuff in the HD free space that did NOT need to be there, stuff that I had deleted, including financial and other sensitive data, but was still recoverable. So I did some housekeeping, removed some large files on the HD to make more space, emptied the trash, and then did a Disk Util. 7-Pass Erase of Free Space. I now have 47 gigs out of 119 free:

I then did another DR3 "Deleted Files Scan", but the results showed up as follows:

After Disk Util. "7-Pass Erase of Deleted Files": 6,102 files recovered from HD by DS3.

A tech at DS3 said this was an abnormal recovery from zeroed-out free space on my HD, and could not offer any DS3 explanation for this result, and suggested I try the "Zero Out" option, which I did, but the results were pretty much the same again:

After Disk Util. "Zero out Deleted Files": 6,075 files recovered from HD by DS3.


1) Anyone have an explanation for this?

2) Is a restart required after using DU to free space?

3) Are there any known issues/bugs with using Disk Util. to clear free space, where the deleted files are not successfully written over?

4) Is there any way, using the OS X system (or some other method that does not require buying more utility software), that I can confirm the results of the DS3 scan?

5) If there is, and I confirm that I still have 6,000 undeleted files, what then??

I'm not ready to migrate to Lion yet—too many outstanding issues—but open to whatever you can otherwise suggest. Thanks much.


macrumors 6502a
Jun 26, 2007
How long did it take? It sounds it completed the process quite fast, which is totally un-expected.


macrumors newbie
Original poster
Apr 21, 2012
Are you asking how long it took to do the Disk Util. operations?

7-Pass I left on overnight, so I don't know.
The Zero out took about an hour, maybe a little more.

Is there some way I can test operation of Disk Utility to see if it is finishing clearing space within expected time?

Checked back again with DS3 and they are referring me to Apple tech support.


macrumors newbie
Original poster
Apr 21, 2012
Here's the DU log entries (both show successful completion):

2012-08-29 21:37:44 -0700: Disk Utility started.

2012-08-29 21:39:03 -0700: Preparing to Secure Erase Free Space : “Macintosh HD”
2012-08-29 21:39:03 -0700: 7 Pass Erase Free Space
2012-08-29 21:39:03 -0700: Creating temporary file
2012-08-29 21:39:07 -0700: Securely erasing file
2012-08-29 22:51:27 -0700: Creating temporary file
2012-08-29 22:55:33 -0700: Securely erasing file
2012-08-29 22:56:28 -0700: Mounting disk
2012-08-29 22:56:28 -0700: Secure Erase Free Space completed successfully in 1 hour, 17 minutes.
2012-08-29 22:56:28 -0700: Erase complete.
2012-08-29 22:56:28 -0700:
2012-08-30 09:00:40 -0700: Disk Utility started.

2012-08-30 09:54:31 -0700: Disk Utility started.

2012-08-30 09:58:08 -0700: Preparing to Secure Erase Free Space : “Macintosh HD”
2012-08-30 09:58:08 -0700: 1 Pass Erase Free Space
2012-08-30 09:58:08 -0700: Creating temporary file
2012-08-30 09:58:12 -0700: Securely erasing file
2012-08-30 10:30:30 -0700: Creating temporary file
2012-08-30 10:39:40 -0700: Securely erasing file
2012-08-30 10:45:03 -0700: Mounting disk
2012-08-30 10:45:04 -0700: Secure Erase Free Space completed successfully in 46 minutes.
2012-08-30 10:45:04 -0700: Erase complete.
2012-08-30 10:45:04 -0700: