Tiny Code

Tiny Code

Sunday, July 6, 2008

Recovering data from a failing hard drive

I've been trying to recover the data off a failing hard drive for a family member. I've found a few programs which claim to be able to do just that but they always get hung up by the numerous retries the drive keeps doing in the failing areas. Then I came up with the idea of using the dd command to make a copy of drive image which I could then manipulate having gotten the retries out of the way during the initial copy process. I'd used dd pretty heavily during the development of an SD card driver I'd done at my last company. Once the drive image has been copied to a file, the resulting image file can be mounted using the mount command... well it can on Linux and Mac OS X at least. You poor folks running Windows are out of luck.

After looking around on the web, I discovered a great little program called dd_rescue which does intelligent retries if errors are encountered, slowly lowering the block size being requested to find the boundaries of the affected area. I think the standard dd command would try to do retries until the read worked or until the copy was aborted. dd_rescue also allows an offset to be specified when the command is invoked so the copy may be done in several stages. Since it's taken about 4 hours, off and on, to copy the first 33 GB from the failing 60 GB drive, I'm anticipating having to make heavy use of this feature to complete the copy process over the next day or two.

I made a few minor changes to the source to allow me to curtail the retries to speed up the copy. So far it's copied about 32 GB from the failing 60 GB drive. Once the data has been copied then I'll start trying to recover files from it. Wish me luck, I think I'm going to need it!

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