backing up cards whilst out and about

whom said:
As I understand it, when a card becomes corrupted (or hard drive for that matter) it is usually the index that tells the camera/pc etc where each picture is in the flash memory. When you quick format, this index is cleared so the camera will go ahead and put photos onto the card and their locations will be stored in the blank index . It will infact be overwriting the image still stored in the memory. The same probably applies to deleting an image, it just removes it from the index.

So as long as you don't continue using a card and overwrite the data with new pictures, the old pictures are still there but there is no index to find them. Instead the pc has to trawl through every bit of memory piecing the data together.

I think of it as a library full of books and a book at reception telling you where each book is. This library runs a policy of "if it's not in the book in reception and you need to put your book on the shelf then throw the old book out"
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That was my understanding of it too Steve, but my son (who is far more technically mind than myself!) plugged the card into his Mac and brought up thumbnails of every single image I'd ever taken on that card, sorted by date. The file could then be copied to the computer and converted back to RAW.
He's at university, but I'll ask him what the program was called. ;)
 
Possibly Photorescue

http://www.datarescue.com/photorescue/v3/index.htm

I've used the same maker's data recovery tools for the Mac for years and it's got files back for me from some seriously borked drives.

Sandisk used to bundle a free recovery app with their higher end cards, though I'm not sure if they're still doing that.
 
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HutchyP said:
That was my understanding of it too Steve, but my son (who is far more technically mind than myself!) plugged the card into his Mac and brought up thumbnails of every single image I'd ever taken on that card, sorted by date.
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In which case you hadn't taken many photos on that card.

I have a card 4GB that must have taken over 5000 images. Do you really believe all of those images are still accessible?
 
hunnymonster said:
Yes, plus the power supply - if weight is that tight I'd just take even more memory cards... my pockets aren't limitless :'(

Anyway - when the RasPi arrives it's tasked with being netbook replacement for this task... only need it to boot, autocopy the contents of the memory card (from the reader attached to the USB to the HDD attached to the USB) - net requirement one USB power supply...
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Is the USB power supply going to be beefy enough to supply a card reader and a HDD at the same time? Might be a powered USB hub is required.
 
We shall see - the fun of experimentation :)
 
Paul, if every photo ever taken on a card could be recovered then we would have infinite GB cards by now. I believe that the card is written from start to finish to even out the wear on the memory chips. So even if you wipe the card, the card still writes the data from the same point it would have done if you hadn't wiped it. So if you've have taken less pictures than there is space on the card then in theory, no matter how many times you've wiped the card, all pictures could be recovered.

What I suspect is that whenever you recover a well used 8gb card (for example) then you should retrieve the last 8gb of photos taken on that card.

I might be wrong but I don't think for one second you could recover a part of the memory that has been overwritten by another picture.
 
hollis_f said:
In which case you hadn't taken many photos on that card.

I have a card 4GB that must have taken over 5000 images. Do you really believe all of those images are still accessible?
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Ok, so I was slightly wrong. The program he used worked directly from DOS on his Mac and simply reads and converts the cache files on the card. The card in question had had over 12000 images written to it in it's life, and most were visible - and yes it took a while to sort through them.

Here's a link to the program, hope this helps ;)

http://www.cgsecurity.org/wiki/PhotoRec

Obviously as the cache grows the useable space shrinks, but I can still fit hundreds on that card so I'm not worried at the moment!
 
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There's no such thing as 'cache files'. When you write an image to the card the actual data is written to different areas of the memory. An entry is added to the 'File Allocation Table' (FAT) that lists just which bits of memory are allocated to that image. When the next image is writ the card's controller knows not to use those bits of memory, so it writes the image data to unused areas of memory and puts that info into a new entry in the FAT. And so on.

When you delete an image, no real data gets deleted. The image's entry in the FAT gets altered to tell the controller that the memory areas used by that image are now free. When the next image is written those areas may, or may not, be used. After a while the result is a card with a lot of images with entries in the FAT and a lot with FAT entries that mark the memory areas as free for use.

Recovery software will look at the old FAT entries for deleted files and recover the image if those areas have not yet been overwritten. With 12000 images most of them will only have fragmented data (12000 images would be around 300 GB for raw images and about 60 GB for jpeg). If you managed to get all the image data for most of those 12000 images then congratulations are in order as you've just broken several laws of physics.
 
Well as I said, I'm no expert in this field. I'll run the program again when I get time to see if it works again.
 
digital said:
Keep them both with you. Netbook in your carry-on luggage and, if carry-on weight is an issue, put the external hard drive in your pocket.

If you don't have enough pockets then have a look at item number 280617132602 on Ebay. I used one on a few flights recently and it held a lot of quite heavy items...
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I have done this before. EasyJet wanted to charge me for the extra weight of my carry on back. I had to put lenses and the flash gun into my jacket pocket :)
 
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