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Re: [Bug-ddrescue] input/output error when mounting ddrescue output .dmg


From: James Wilson
Subject: Re: [Bug-ddrescue] input/output error when mounting ddrescue output .dmg file
Date: Fri, 18 May 2012 10:39:08 +0100

Hi Nate,

I recently had to utilise the amazing ddrescue to recover an encrypted 3TB FileVault2 drive.  The image alone took 2 weeks to create, so I feel your pain!  Mounting the DMG via Finder was problematic, however via the console gave more positive, but mixed results.

I ended up, as suggested by Felix, writing the image back to a known good drive via a CentOS 6.2 box.  This worked perfectly, using the command:

ddrescue -v --block-size=4KiB ./sda.dd /dev/sda recovery_drive.log -f

In order to help you, could you provide the following information

- What version of ddrescue?
- What command line syntax did you use to create the image?
- Was the drive a single partition, using HFS+?
- How did you try and mount the image, via Finder or the console?
- If the console, what was the command used?

Kind regards,

James


On 18 May 2012, at 09:18, Felix Ehlermann wrote:

Dear Nate,

I think you might be writing to the wrong list, but I can give you a few generic advices, hoping that they will be of help to you:

* If you create an image from a damaged drive, DO NOT perform repair-operations on this image, but make another copy (e.g. dd the image onto a working drive) and try to repair that copy. This way you will not lose additional data if your repair tool screws up, because your first (44 hours worth) copy is still preserved without any additional damage.

* It is not obvious to me which instructions you were following, and it is also possible that you made a mistake when typing / copying the commands - so in general its a good idea to provide the command line you ran and maybe some output (was all data recovered? were there unreadable sectors? etc.). This way people can better understand what you did and give you more specific support.

Regarding your problem to open the dmg-file I would assume that you maybe copied the entire drive's content into the image - including the partition table. This might prevent the dmg-file from being directly accessible (because the partition table is 'in the way'). The error message seems to indicate a different cause (as it doesn't complain about the content of the file but about an i/o-error), but (fortunately) our Mac customers didn't provide me with this kind of problem yet, so I don't have further suggestions on this.
If my guess about the partition table is correct, you might be able to access the data after copying the image back onto a working drive - but (as you didn't provide additional information) it's of course also possible that a major part of the drive was not readable and you will need to repair the filesystem structure first. For that you will need tools other than ddrescue.


Kind Regards
Felix

On 16.05.2012 18:45, Nate Wood wrote:
Not sure if this is the right forum to ask as this is not a bug so I apologize if it is not.  Just desperate for help at this point.

I used ddrescue for a Mac server and created a 445GB .dmg file as the instructions showed how.  However, when I continue the instructions and try to mount I get this error:

mount_hfs: Input/output error


I can do some digging of course and will but after waiting 44 hours for this file to be created my heart sank when I got this message.

If anybody can help I'd appreciate it.  And if this the wrong forum please let me know that too.

Thanks.
Nate


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