Recovering data using "dd"

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Level 3

606 points

Recovering data using "dd"

Hi,

I'm using this tip from MacOSXHints to try to recover data from an external drive attached by FireWire. It essential involves using "dd" in the terminal to perform a bit-by-bit transfer of data from a failing disk to a disk image on a healthy one. The command is as follows:

dd bs=512 if=/dev/rdisk1 of=~/Desktop/Recovery.dmg conv=noerror

Unfortunately, this command returns only a "device not configured" error. The following command

diskutil -mountDisk /dev/rdisk1

reports success, but *diskutil list* only reports disk1 as having 0 bytes and no partitions, even though it is 80GB in size and has two partitions.

The drive in question is reported as unreadable by the OS and I'm given the option to format. Is this drive truly unrecoverable now (without spending a great deal of cash on a professional service)?

By the way, I would have added this query to the foot of the MacOSXHints thread, but it hasn't received a response in a while, so Apple Discussions seemed a better choice.

Many thanks,

SiR G.

MacBook Pro MB470LL/A, 4GB RAM, Mac OS X (10.6.4), ; iMac 20" MA876LL 10.6.4; iPhone 3GS 16GB iOS4.0.2; AEBS MA053LL/A

Posted on Dec 7, 2010 1:37 AM

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Answer 1

etresoft

Level 9

56,212 points

Dec 7, 2010 5:30 PM in response to SiRGadaBout

Even if you were able to extract all the bits from the device, it would certainly be a corrupted file system and corrupted files. What would you do with it?

If you really want to get the data, I suggest contacting the two companies listed in this document for a quote: http://support.apple.com/kb/HT3974?viewlocale=en_US

There may be other companies that provide this service, but these are certified by Apple to disassemble your drive without voiding your warranty. One person who used one of these companies was quoted a worst-case price of $800. In her case, it was much less than that because the drive was actually damaged beyond repair.

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Answer 2

Lurch66

Level 1

30 points

Dec 7, 2010 1:47 PM in response to SiRGadaBout

I've had to recover data from seriously fubar'd hard drives, but only the following has worked (minus the %):

% cp -npRv "/Volumes/Folder" "~/Destination_Folder"

It will copy any/all data it can, and not error out when it gets stuck

But if you can't even see the source data using Terminal, then this probably won't work at all

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Answer 3

Linc Davis

Level 10

209,739 points

Dec 7, 2010 3:43 PM in response to SiRGadaBout

I'd guess that you're much more likely to have success with either GNU ddrescue or dd_rescue (different things), or with one of the commercial disk-recovery products, any of which is designed for the task, while dd is not. You can install ddrescue or dd_rescue free of charge using MacPorts, after first installing Xcode. Or you can search for a term such as "rescue" on one of the Mac software repositories such as macupdate. Those solutions will cost something, but a lot less than a recovery service. However, if the data on the drive is worth more to you than about $10,000, don't mess around with it. Send it straight to somebody like Drivesavers. Anything you do carries the risk of making things worse.

The real point is that you should never need to recover a drive. When a drive fails, the right approach is to destroy it and restore to a new one from one of your several backups.

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