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Saturday, 14 July 2007

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Great to hear you manged to recover most of your photos.
I hope you won't have this kind of worry again!

Of the 3 that worked - did you have a preference regarding how it did it's job, ease, interface or perhaps free(?), that would set it above the others?

I've had excellent results with Restorer 2000, on disks that the other programs were completely flummoxed by. It can take upwards of 8 hours on a dual processor 4 gig machine to to find the files on a 200gig drive, but that's after the file allocation tables and boot records were so corrupt that other programs wouldn't even recognize the drive.

It is important to realise that any photo recovery software will have the best chances of getting back your images if you stick to these few rules:

- Always format the card in-camera at the beginning of each shoot (I mean "format", not "delete all" - there's huge difference)

- Never delete a photo in-camera, files will be written sequentially that way.

- Never write to the card on your computer - let your camera be the only thing that writes to it.

These hints all have to do with the layout of the file-system. For instance - a file that's deleted is removed from the directory listing and the space previously taken up by it is marked blank, although the data is still there. That way the card's file-system gets fragmented by these holes. Subsequent files might not be written in one piece, but split up over a couple of these holes, thus overwriting the hidden data left by the deleted images.
Photo recovery tools will have a hard time piecing together fragmented files - most fail at that.

In short:

A file-system that's filled up from a clean start (freshly formatted) in sequential order by each new file will be easiest to recover.


These hints are quite old and repeated frequently on the net. If anyone has new information of how the algorithms in modern cameras might have changed, please come forward. I am no expert on file-system technology.

if you look at the wikipedia entry for cf cards they describe a technology called wear leveling-essentially the card has a fixed number of read/write cycles and the file system attempts to avoid writing data in the same location over and over to spread the wear out. I think this means that any idea of data being actually written sequentially on cf cards or indeed on hard drives too is a fallacy. All of the hints assume computers are more like humans than computers, they are quite happy writing data all over the drive and today their is little performance penalty, the access is so fast.

But I will throw one hint into the fray-I have been choosing to shoot raw+jpeg now for a while with the idea that if I have a card failure, I have twice the chances of recovering an intact photo. Fortunately I have yet to test this...

Dear Chris,

All three that worked for me were free, and none of them were rocket science to use.

pax / Ctein

Dear Robert,

Hard drives and flash RAM are very different beasts. While it is possible to wear out magnetic media (I've seen core memory that actually got worn out!) the mechanical components of a hard drive will have ground themselves to dust long before that will ever happen.

In fact, contiguous file access is still a factor in hard drive performance, which is why OS's do disk optimization. If it has any effect on disk life, it is to increase it, as optimization reduces the number of head repositionings.

pax / Ctein

When I accidentally deleted all of my wife’s data – including documents and pictures – SanDisk’s RescueProTM saved my hind end (and probably the rest of me). It managed to recover everything in fairly short order, including my marriage. And it’s free.

Chris
http://christopherwlane.blogspot.com/

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