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Re: Problem using dd to clone a hard disk with bad sectors.

Subject: Re: Problem using dd to clone a hard disk with bad sectors.
Date: Mon, 20 Feb 2006 09:33:41 +1300
Willard Van Dyne wrote:
I'm trying to properly clone a 4.3GB (it's old, I know) hard disk which unfortunately has a lot of bad sectors.
I am using Helix 1.7 as an operating environment, not mounting the old drive at all.
I used the command:


dd if=/dev/hdb of=/mnt/hda7/image.dd conv=noerror,sync

My problem is that the md5 hash of the image file is different from that of the original HD (acquired via the command: dd if=/dev/hdb conv=noerror,sync | md5sum > /mnt/hda7/orig_disk_md5sum.txt)

Can anyone please enlighten me as to what I'm doing wrong?

The drive has bad sectors. Why do you think the original MD5 is meaningful? Have you tried to reproduce that MD5 by re-hashing the original drive? Chances are that you won't be able to reliably obtain the same MD5 hash code when you hash the original drive. The bad sectors are unpredictably-read, and your hashing tool doesn't exclude them.


If you can get a map of the bad sectors then you could use a different hashing tool to hash just the good sectors, and in this way come up with a meaningful MD5 hash.

Best,

Jason Coombs
jasonc@science.org

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