[ale] semi [OT] help recovering data from memory card

[Ron Frazier]

Hello all,

I have completed the recovery of the pictures.  Thanks very much for all 
the suggestions.  There were some interesting twists to the story.

First I used the dd command below to make an image of the faulty SD 
card.  I had placed sudo in front of the command.  I don't know if that 
was a mistake, but, after dd finished with the image, the file was 
locked and owned by root.  I had to use the sudo chown command to change 
the owner and group to my name.  Other than that, there were no errors 
with dd.  I then removed my relative's memory card and copied the new 4 
GB image file from my desktop to another memory stick I had.  I moved 
the memory stick to my Windows machine and ran PhotoRec on THAT memory 
stick, which had the image file on it.  I could have run it on the Linux 
system if I'd wanted, but I'm more familiar with file operations in 
Windows.  It recovered 371 photos, which, as far as I know, was all of them.

Another somewhat eerie thing happened.  There were no files showing in 
the directory of the second memory stick I was using, other than the 
image file I stored there.  PhotoRec also recovered another 30 or so 
other files, of several other types besides photos, that had been on 
that memory stick long ago and were mine and had been deleted.  I know 
they never really get deleted, but it was really strange seeing them 
come back from the dead.

Just for fun, after saving the photos we wanted to keep, I went into 
Windows Explorer and selected the memory stick an formatted it, being 
sure to turn off the check box that says quick format.  I then ran 
PhotoRec again on that memory card, just to see what would happen.  In 
this case, PhotoRec was unable to recover any files, which is what I 
hoped would happen.

I didn't get to try the other program that was suggested, but I 
certainly appreciate that suggestion as well.  So, thanks everyone for 
all the help.  This was an interesting learning experience, especially 
the part about my files coming back from the dead.  So, be warned, if 
you put any sensitive information on a memory stick, if you don't want 
it showing up later, you'd better truly format or wipe it.

Sincerely,

Ron

On 10/19/2011 9:59 AM, Michael H. Warfield wrote:
> On Wed, 2011-10-19 at 09:21 -0400, David Tomaschik wrote:
>    
>> On Tue, Oct 18, 2011 at 9:37 PM, Michael H. Warfield<mhw at wittsend.com>  wrote:
>>      
>>> On Tue, 2011-10-18 at 08:51 -0700, Boris Borisov wrote:
>>>        
>>>> I'm going to follow this post carefully because I have to deal with
>>>> the same problem :) missing partition information. Actually dmesg
>>>> gives me message : sd 1:0:0:0: [sda] Assuming drive cache: write
>>>> through
>>>> sda: unknown partition table
>>>> What I am doing now is dd if=/dev/sda of=usb8gb.img just in case. Will
>>>> take a while with this USB.1.1 that I plugged into it :)
>>>>          
>>> If you get a hard failure, you may want to try dd-rescue on it.  That
>>> will work around "holes" in the data and continue to recover data.  It's
>>> what I use for hard drives, though I don't know how well it will work on
>>> USB flash drives.
>>>        
>    
>> I'm not sure whether or not dd-rescue has any benefits on flash media.
>>   I would think that blocks on flash media are either functional or
>> dead.  (The idea on dd-rescue being that the disk might be able to
>> read it on a retried pass.)
>>      
>    
>> Adding the conv=noerror option to dd, however, should have no downside
>> and has the upside that blocks AFTER the unreadable block will be
>> read.
>>      
> The main advantage, in this case, that I see, is that it uses a divide
> and conquer methodology where it tries to read large blocks and, if it
> gets an error, it divides down into smaller blocks and tries to divide
> into large blocks of errors looking for smaller islands of working
> blocks.  I suppose that dd with conv=noerror and a minimum block size
> would probably work as well.  I wasn't considering the retry option
> there although one probably shouldn't discount thermal problems.  I've
> had some flash drives that would sometimes read and then sometimes not.
>
>    


-- 

(PS - If you email me and don't get a quick response, you might want to
call on the phone.  I get about 300 emails per day from alternate energy
mailing lists and such.  I don't always see new messages very quickly.)

Ron Frazier

770-205-9422 (O)   Leave a message.
linuxdude AT c3energy.com