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Should memory cards in DSLRs be formatted every so often? If so, how often?

I hear that after emptying the card out (transferring images to a computer), that it's a good time to format it to help reduce the chance for error/corruption. Is this true?

I want to point out: Nikon D90 User's Guide by Ken Rockwell

From the site:

Always format your card after you put it in any camera, or if you've connected your camera to a computer.

Formatting your card(s) ensures any folder or file corruption acquired anywhere goes away.

You can shoot without doing this, however constant formatting is good practice and should eliminate ever having any card errors. Be sure you've downloaded and backed up all the files in two different physical locations before formatting.

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Nikon is covering their rear end, there's no technical reason for this but lets them out if you have an issue with a card and contact them. Let me put it this way, the most likely source of corruption would be your camera... –  John Cavan Aug 4 '10 at 20:28
    
Correction, I assumed you linked the official Nikon guide... That's Ken's opinion, not an absolute. –  John Cavan Aug 4 '10 at 20:34
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Ken Rockwell is absolutely wrong in saying that this " should eliminate ever having any card errors". It will help correct one (rare in practice) class of problems, but not everything else. –  mattdm Mar 27 '11 at 19:53

7 Answers 7

up vote 27 down vote accepted

I format my card every time I stick it in my camera and start a shoot.

I do this for a couple of reasons.

First, it means every time I start a shoot, I don't accidentally leave the previous shoot on it (and it also means I don't delete it until I start the next shoot, by which time those images are safely on various backup disks; gives me an emergency backup on the card until I'm sure I've got multiple copies elsewhere).

Second, I use multiple camera bodies, and I know people who've had corruption issues with cards formatted by the computer (which I never do) or by one body and used in another because the bodies interact with the card slightly differently. By formatting every time, I know the formatting is what the camera wants and is expecting.

Third, formatting at the start of the shoot will (or should!) catch a card that is starting to fail. At the least, it'll catch some early failure modes in the card -- and in two cases for me so far, it has. So if the card hits an error during format, I know to immediately retire it. I'd rather find out I have a card error at the START of the shoot that midway into it, or worse, when I'm trying to read the images out later.

Note: any time I get a card error, I retire that card. Cards are cheap. Dead cards that eat my only copy of an image is expensive. And formatting a card every time means that every time I shoot gives me a blank slate in a known state that hasn't reported an error. Which means many fewer potential problems later. And FWIW, I basically never run into corrupted cards, lost images or problems during a shoot or during a post-shoot import.

Even if it means the card will wear out sooner, I don't care. I want reliable cards, not ancient ones. I'll happily replace them rather than try to recover images from them....

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+1 but not because I think you need to format like that, but because your reasoning for doing so is well thought out. I also agree that once a card starts to fail, toss it. –  John Cavan Aug 4 '10 at 21:22
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+1 cause I do the same thing –  Josh Goldshlag Aug 5 '10 at 0:13
    
Agreed. Another reason is to correct file system errors that can creep in over time. –  labnut Oct 16 '10 at 20:52
    
I see your point about backup and also catching a failing card, which I hadn't thought of. –  Håkon K. Olafsen Feb 23 '12 at 18:53

I would see no reason to format the card on a regular basis, simply erasing all images on the card is sufficient. Bear in mind that most flash based media have a limit on the number of writes and so formatting is going to help you reach that limit a little bit faster.

The only upside to formatting, which is probably where this idea came from, is that it can be faster than file delete. That I might do if the card was full or close to it. However, if I'm transferring anything less than half the capacity of the card, I'd probably just erase the files afterwards.

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Agree with John. I formatted my card once (in the camera) prior to using it the first time. –  Johannes Setiabudi Aug 4 '10 at 20:18
    
I added a reference to Ken Rockwell's site where he recommends formatting. –  sunpech Aug 4 '10 at 20:26
    
@sunpech: In both our cases, it's opinion. Obviously, I disagree with him, though. –  John Cavan Aug 4 '10 at 20:33

The camera will only ever do a "quick format" as there is a limit on read/write operations on flash memory.

Personally, I use several cards in rotation, and format immediately prior to needing it again -- the benefit of this approach means that when my hard disk died last year, I didn't lose any files, as I could download from card again (and restore older pictures from backups)

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The first thing I do is copy to two different drives (one internal and one external) and, once sure that both have it, I'll erase. –  John Cavan Aug 4 '10 at 20:31
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@John I'm insanely paranoid, as I back up to 2 DVDs as well, and keep the DVD sets in different towns, too... –  Rowland Shaw Aug 4 '10 at 20:45
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That's a pretty good definition of paranoid! –  John Cavan Aug 4 '10 at 20:47
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@John I learnt a few years ago that you really do need to test your disaster recovery strategy with a dry run occasionally. I was glad I'd been paranoid last year though :)... –  Rowland Shaw Aug 4 '10 at 20:58
    
I believe that you don't actually have a backup unless you have tried and succeeded at a recovery. You do want to test that on purpose when things are calm, not after a burglary, fire, flood, or quake. –  RBerteig Aug 4 '10 at 23:36

Memory cards are FAT formatted. When a file is deleted in FAT, the space is marked as free, but there can still be hidden fragmentation and corruption. Formatting rewrites the allocation table to make sure the space is continuous and you don't have any file-system errors.

As a precaution, I do it every so often especially when burst shooting when I never want to be limited by write speed.

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As memory cards have random access, fragmentation should not be a problem. –  Guffa Aug 4 '10 at 20:34
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Also, fragmentation on a FAT file system is more common when deletion is scattered. If you empty the filesystem with deletes then fragmentation isn't a concern. Besides, the biggest issue with fragmentation was because DOS was a dog and older hardware could only handle one I/O request at a time. –  John Cavan Aug 4 '10 at 20:52
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Also, if you delete every file there will never be fragmentation. Fragmentation only happens when free blocks are mixed with use blocks, which only happens when you delete some files but keep some around. –  SoapBox Aug 4 '10 at 20:54
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@Guffa: lack of fragmentation is why class 2 (based on slowest speed) can perform at class 10 speeds at times: The memory of a card is divided into minimum memory units. The host writes data onto memory units where no data is already stored. As available memory becomes divided into smaller units through normal use, this leads to an increase in non-linear, or fragmented storage. The amount of fragmentation can reduce write speeds, so higher SD card speeds help compensate for fragmentation. sdcard.org/developers/tech/speed_class lagom.nl/misc/flash_fragmentation.html –  Eruditass Aug 4 '10 at 22:23
    
@John see my link above. Fragmentation is a major issue and that is why class numbers are calculated on the slowest most fragmented speeds but often perform better. @SoapBox: In theory, yes, who knows what kind of metadata and allocation table modifications are done throughout its use on different devices? I just play it safe, that's all. –  Eruditass Aug 4 '10 at 22:30

Yes, memory cards should be formatted now and then, but it doesn't have to be very often.

If you format it every time you empty it, you will perform write operations to the same part of the memory, which shortens it's life span. So that would actually in the end cause corruption instead of fixing it.

When you delete files, the data is left on the memory card but marked as reusable. When you create new files it will first use sectors that hasn't previously been used, so this will spread the usage so that new files aren't always created in the same place, which prolongs the life time of the memory card. When you format the card, this information is removed. So if you format the card each time you empty it, new files will always be created in the same part, also reducing it's life time.

Formatting a memory card doesn't reduce the chance of corruption, a newly formatted card is no less prone to get corrupted. It will however fix corruption if it's already there.

When you create and delete files on the memory card, the directory entries are not removed but left to be reused. Over time this can accumulate, and formatting will regain this space, but generally it's only a few kilobytes so it's certainly no reason to format often.

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the card's firmware should spread writes around the memory in a way which minimizes rewrites, to minimize this wear. So even if you write to the same logical sector again, it doesn't necessarily map to the same physical sector. –  Reid Aug 4 '10 at 20:40
    
@Reid: Interresting, that would reduce the wear of some memory cards significantly. –  Guffa Aug 4 '10 at 23:44

I format my card in-camera before every use. I use the USB cable and never take the card out of the camera unless I fill a card on a long shoot/trip. I've never had a problem, but I can't say that's because of my procedure. Seems to be a lot of hearsay about what the correct procedure is :)

So here is what some manufacturers have to say.

Nikon

Memory cards need occasional maintenance, too. Every Nikon digital camera offers an in-camera format option. Formatting the card in-camera not only deletes the pictures, it creates a new directory on the card. This can help to avoid problems that might prevent the card from being read by your computer. Some people format after each download, once the photos are safely transferred to the computer. Others choose to do it once a month. The important thing is to do it regularly.

Olympus

Memory cards should be formatted to maintain top performance. They should only be formatted using the camera—never format using a computer as it may render the card unreadable by the camera.

Formatting clears the directory structure of the card and removes any artifacts that might be left behind by erasing. Repeatedly using the ERASE and ERASE ALL camera options and not formatting can result in a buildup of file artifacts that may eventually cause the card to fail. Be sure to download and save any images on the memory card before formatting

Sandisk (refers to Mac)

When using a memory card, it is recommended to reformat the card in the camera instead of formatting it through your computer

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+1, but my suspicion is that these statements actually add to the superstition via oversimplification. The manufacturers' motive is to reduce their support calls. I think there's probably no problem at all if you format out of the camera correctly (after all, brand new cards arrive formatted out of camera), but that there's so many ways to do it wrong (wrong filesystem, bad blocksize choices, etc.) that it's much easier for them to just tell us to always do it in-camera. –  mattdm Feb 23 '12 at 17:52
    
Another possibility is formatting on a computer then pulling it out without using Safely Remove Hardware which I'm sure many people do. Not sure how likely that is to result in errors on the card. –  MikeW Feb 23 '12 at 18:29

I use my computer to delete photos from the card after importing them. I NEVER reformat the card. For me it is useful to not reset the camera's image counter that generates the file names for images on the card. This lets me add images to my photo gallery on my computer without file name collisions.

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Most cameras have an option to retain the image counter even if you reformat the card. –  mattdm Feb 23 '12 at 17:28

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