Corrupted CR2 file out of the camera

[groman]

I have a 7dii bought new 6 months ago- I have gotten three or four files that came off the camera corrupted. Why is this happening and should I worry about it? So far it hasn't seemed to affect any important shots, but I will know I will be dissapointed if it happens to a great shot.

[Waddizzle]

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@groman wrote:

Thanks very much- I will try formatting the card in camera. I regularly delet shots directly from the camera- didn't realize it was a bad idea.

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It could be bad if you have never formatted the card yourself.  New cards should always be low level formatted prior to first use.  New cards are not pre-formatted.  They are tested during production, and what seems like formatting is actually residue from production testing.  

I have never had problems deleting files in the camera, but it is usually the most recent shot that I took.  Deleting files just erases the entry in the storage medium’s directory.  The actual data is not overwritten or erased, but it can be if you write new data to the card.

As far as low level formatting a camera goes, I have to question what it is that the camera does when it supposedly performs a low level format, because the camera does it WAY too quickly.  A computer spends a LOT more time performing a low level format on a memory card than your average camera. Use a card reader and try it some time, but do not use a high capacity card if you do.

I do not think cameras actually test every storage bit.  I think they just go through and erase the pointers in storage blocks.  The file directory points to the first storage block of a file, and at the end of each block there is a pointer to the next storage block.  This continues until the final storage block, which will have an “End Of File” code, instead of a pointer.  I think cameras simply erase the pointers, which makes it near impossible to recreate the storage path of a file.

[Peter]

This is a part I don't really understand, but SD cards support ERASE command to be able to erase everything at the same time. Probably that's why it is so much faster than doing a normal "low level format" in computer.
I also guess the low level format in camera maps out bad sectors.

A CF works differently and doesn't have low level format in camera.

[groman]

Lots of good information- thanks everyone. I realize the CF card I am using is the one from way back to my 40D, so I'm betting it is getting a bit tired. I think it's time for a new card, which I will format before use and regularly after. Is there any preferences for either CF or SD card?

Thanks again all!

[Waddizzle]

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@Peter wrote:
This is a part I don't really understand, but SD cards support ERASE command to be able to erase everything at the same time. Probably that's why it is so much faster than doing a normal "low level format" in computer.
I also guess the low level format in camera maps out bad sectors.

A CF works differently and doesn't have low level format in camera.

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I have to question what exactly a camera does when it low level formats an SD card.  If you assume a continuous write speed of 33 MB/sec, then it should take 30 seconds to write just 1 GB.  At that rate, then it should take 16 minutes to “low level format” a 32 GB SD card, which is about how long your PC would take to do it.

But, a camera seems able to do it in well under a minute.  And, 16 minutes does not include to Read the test data back.  I think all a camera does is initialize pointers in the storage blocks, and clear any block allocation table.