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Re: [Bug-ddrescue] Help rescuing my 500GB disk


From: Scott Dwyer
Subject: Re: [Bug-ddrescue] Help rescuing my 500GB disk
Date: Mon, 11 Nov 2013 18:12:33 -0500
User-agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:24.0) Gecko/20100101 Thunderbird/24.1.0

I would like to point something out that relates to both an "unfinished" image, and using ddru_ntfsbitmap (something I need to add to the documentation). In any event, anything less than a 100% recovery will leave portions on the target image/drive that have not been written to by ddrescue. If copying to a brand new hard drive, those areas are (hopefully) likely to be zeros. But in any other case, those areas will contain whatever data was there previously. For someone that uses their system for data recovery on a regular basis, and is using image files or reusing hard drives, those areas could contain data from a previous recovery! This could be a privacy issue in some cases, but also could cause an issue with running any other sort of repair/file recovery tools on the recovered image/drive. The unrecovered parts could contain "garbage" data that could affect accurate recovery. In these cases I would recommend using the fill mode of ddrescue to fill any unfinished/untried areas with zeros.  Example command:
ddrescue --fill-mode=?/*- /dev/zero recovered_image logfile
This would write zeros to any portion of the recovery that was not successfully read from the source.

So now to answer your question about an "unfinished" recovery. That depends on how much and what areas were recovered. You can obviously only recover what was successfully read. In the case of NTFS, if the MFT (master file table) is not recovered in full or is damaged, it makes recovery much more difficult. Which gives me the idea of adding an option in ddru_ntfsbitmap to create a secondary domain file for just recovering the MFT first :)

Scott


On 11/11/2013 12:22 PM, Andrej Trobentar wrote:
On 11/11/2013 06:00 PM, Scott D wrote:
I am at work so I must be brief. I see you are using my very new utility ddru_ntfsbitmap. I hope it works well for you. What I do see in your commands is that after a failure, you leave out "-m /tmp/domain_logfile". Leaving that out will cause ddrescue to read the whole partition and not just the used part. So your command after a failure should be more like "ddrescue -A "-m /tmp/domain_logfile -v /dev/sdb1 /tmp/Image.img /tmp/Image.log", unless you do wish to recover the whole partition and not just the used part.

First of all thanks for your fast reply!

OK, I'll add the "-m /tmp/domain_logfile" in case of driver failure - glad I asked first :)

As for mounting, I personally would not try to mount it until the recovery is finished. And if it were me, if possible I would make a backup copy of the recovery before attempting any "fixing" or mounting, especially if there are errors.

Of course I would make a copy of the "unfinished" image and do all the experiments on the copy, but thanks for pointing that out.

But let's assume that the drive doesn't power up any more. How to recover from the "unfinished" .img file that we got left? Is this even possible?


Thanks for your answers and greetings from Slovenia,

    Andrej.




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