I have a 2008 iMac in which the drive is failing. SMART status seems ok although AHT reported 4hdd/11/40000000 SATA (0,0) which is the code for disk failure AFAIK. Normal boot fails, Firewire target disk mode works, however after a certain amount of disk access the drive stops responding - for example in the middle of a large file transfer it never get beyond a certain point. After this folder listing stops working and all I can do is reboot the iMac.

I have read similar questions that suggest using Ddrescue. However the behaviour of my drive is that it doesn't report failure, it just never finishes. Will Ddrescue cope with this?

Update: I've made the question title less specific so hopefully more people find this thread - be sure to check all comments below for some useful tips.

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    Adding this as a comment instead of an answer simply because I am not directly addressing your question wrt using Ddrescue. Instead, I would recommend Disk Warrior. I had a recent external hard drive "failure". The drive was clicking, a typical sign that the drive was on its last legs. I could only access data for short periods of time before it would unmount itself. I purchased DW, and I couldn't figure it out. So I called their support. Their support is fantastic. I spent several hours on the phone with a tech, and he walked me through repairing the drive enough to let me pull the data off. Oct 21, 2013 at 16:15
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    My impression is that target mode doesn't cope very well with failing drives. You may get better results if you remove the drive and mount it directly (or via a USB-SATA adapter or such) on the computer you're doing recovery on. If this gets you normal failed reads instead of complete lockups, you would be able to use ddrescue effectively. Oct 21, 2013 at 18:25
  • Thanks a lot freerangemonkey and gordon-davisson - very useful!
    – MachineElf
    Oct 21, 2013 at 22:02
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    It's probably a little late for this case, but I thought of another way to work around Target mode's limitations that doesn't involve buying an external adapter: put the other (functioning) Mac in Target mode, start the problem Mac with the Option key held down to get the Startup Manager, then boot from the other Mac's HD. You're now booted from a functioning disk, and have direct access to the problem disk to run ddrescue etc on it. Oct 29, 2013 at 3:19

1 Answer 1


Since you're having problems with the drive after using it for a while, no tool may be of help completely. Depending on what's actually failing on the drive, trying to re-read the same sections for a long time could possibly aggravate and expand the problem to other areas. So I would not recommend ddrescue as the first option.

Since there may not be a single solution that is guaranteed to work for this case, I would suggest a combination of different approaches:

  • Try to copy small sections at a time (starting with the most valuable data, leaving aside OS, Applications and Application Preferences that can be redone later with some time on hand) and give it some rest in between.

  • Try the freezer trick to see if it helps

    • Remove the hard drive from the computer.
    • Place the hard drive inside of a zip top freezer bag. (don't buy a cheap bag.)
    • Place the wrapped hard drive inside of ANOTHER zip top freezer bag. (yes, you need to do this)
    • Place the double wrapped hard drive in the coldest part of your freezer.
    • Leave the hard drive in the freezer for 12 hours at least. You want it good and cold! (see figure 2 below)
    • Once very chilled, install the hard drive in your computer and start pulling off data. Begin with the most valuable data.
    • At some point, the hard drive will fail again. When it does, mark the last successfully copied data, pull out the hard drive, double wrap it again and stick it in the Chill Chest for another 12 hours. You may need to do this a number of times to get all the data you want, or until the hard drive stops working completely.
  • For any data that you are able to copy out, do a quick verification and back it up elsewhere. You can never have too many backups!

  • Depending on the drive's manufacturer, download the hard drive test tool from the manufacturer's site, install it on a USB thumb drive and run it. This may help in detecting the actual issue better while at the same time marking bad sectors so that they're hidden (the latter is possible without these tools as well).

  • As a final measure, use ddrescue to see what you can recover before throwing or recycling the drive.

In the future, ensure you regularly use Time Machine in conjunction with a disk cloning utility (Clonezilla, Carbon Copy Cloner or SuperDuper!)

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    Thanks a lot for the great answer! In my defense I did do TM backups (manually) so I didn't lose everything, only a week or so...
    – MachineElf
    Oct 21, 2013 at 22:08
  • Quick question: Should one try the "freezer trick" before ddrescue?
    – landroni
    Jan 30, 2014 at 11:07
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    Depends on the issue, but trying the freezer trick before ddrescue would be more helpful. Just remember to put it into two layers of bags (bag within a bag) so that no moisture gets in.
    – M K
    Jan 31, 2014 at 15:32
  • @MK Well, some others suggest that the freezer trick can be a quick way to brick modern hardware. (See Are hard drive disks airtight? and Recovering data from a damaged hard-drive: the “freezer trick”.) Before actually putting the drive in the freezer, I would start more slowly either ensuring proper ventilation to the drive, or operating it from within the fridge.
    – landroni
    Feb 3, 2014 at 9:11
  • @MK As for ddrescue, after reading the gddrescue docs, ddrescue initially skips over unreadable or slow-reading areas. After finishing with all the content that was easily read and copied, it returns to the problematic sectors for at most one more read (by default) of a non-read sector. From the docs: "Each sector is tried at most two times; the first in this [copying] step as part of a large block read, the second in one of the steps below as a single sector read."
    – landroni
    Feb 3, 2014 at 9:23

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