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I was reading How formatting an SD card is different on Mac than on Windows? and some of the advice in comments and answers seems to suggest that every time after transferring photos to a PC or Mac (etc) you should format your SD-card in the camera.

Best practice is to copy all files from the card to you hard-drive as soon as possible and then reformat in camera,

I understand the point about only using the camera to do the formatting, but my workflow does not involve formatting the card at all, apart from once when purchased new:

  • Go out and take photos.
  • Return home, take SD-card out of camera, insert into PC.
  • Use PC software to copy image files to PC and delete files from SD-card.
  • Duplicate new images to backup media (NAS etc)
  • Put "empty" SD-card back into camera

Is there any benefit to adding a formatting step to this? It seems like the additional IO might cause extra wear on the flash-memory on the SD card.

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It depends.

As the sentence above was a quote from me, let me elaborate:

While cameras are really good at writing images to an SD card, most of them are only so-so when it come to reading a modified SD card. This includes a card that was formatted in computer as well as making sense of temporary or meta files that were written by a computer.

Some cameras (e.g. my Sony a7 III) even write a little database to the SD card, keeping track of the images. If you then delete images on the computer, the database is not updated, leading to inconsistencies. The camera then complains and tries to rebuild the database, which might fail.

However, your camera might cope well with that and have no noticeable problems.

In the end, formatting in camera is an additional step, that makes sure that the card is in exactly the condition that your camera likes best. So you balance your need of flawless operation of your camera vs some write cycles on a comparatively cheap SD card. It is your choice, but if it saves you trouble just once, it was worth formatting it in camera.

A little side note: If you format a SD card in camera, in a small portion of cameras (e.g. Sony) the format is irreversible. This can be a good thing, so files do not fall into wrong hands if the card is e.g. stolen - but it also means, that you should be sure you really want to wipe the card.

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  • A couple of clarifications. Your side note is misleading. While I certainly haven't verified with all possible cameras, a Long Format of a 64GB ish card would take minutes while a typical Quick Format is only a few seconds and is not irrecoverable. That said, both Windows and Mac's write a hidden file to media (like a memory card) upon plugging it in (Linux does not). This is a common behavior so cameras should ignore these hidden files, but a typical Quick format will eliminate these hidden and undesired files. – user10216038 Mar 18 at 19:26
  • Definitely do not delete images on the computer. Perform all deletions on the camera due to possible index/tracking/DB files that may be present as stated. – user10216038 Mar 18 at 19:34
  • @user10216038 The formatting in the Sony a7 is irreversible. If you use that, the files are gone for good. – Kai Mattern Mar 18 at 20:25
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    I haven't tried a Sony a7 but I used to do Computer Forensics. Unless the format takes several minutes, I'm betting I could recover the files. – user10216038 Mar 18 at 21:29
  • @user10216038 Of course I do not know if you have specialized tooling, but from all the accidents I heard of, no one was able to use the usual data rescue products after their format. See the link - a lot of helpful answers with pointing to data rescue software - but all users that specifically said, they tried it on a sony formatted card say no success. I am not sure what they do, the formatting of a 128 gb card is around 15 seconds - but it is not just a deletion of the file allocation table. sonyalphaforum.com/topic/… – Kai Mattern Mar 18 at 21:53
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Beyond the particulars of each specific camera and how they may handle cards formatted on other devices, there are also benefits to regularly formatting flash type memory.

Bad sectors are mapped out by the card's controller.

Most memory cards have a bit more memory than their listed capacity. When a bad sector is identified, the memory controller will block the use of the bad sector and replace it with some of the 'spare' memory on the card. One of the common differences between top name brand memory cards and generic/no name memory cards is the number of bad sectors mapped out of the card's total memory before it leaves the factory. The greater the amount of memory that must be mapped out, the less reserve memory is available on the card for the controller to use as other sectors fail later on. All of the major brands (Lexar, SanDisk, Transcend, Kingston, etc.) get their components from the same handful of suppliers that actually manufacture the memory chips and controller chips. So do the off-brand names, but they usually buy the leftover components that may or may not have been good enough to pass the QC of the major brands' buyers. One of the thing the buyers look at is how much reserve memory remains on the chips after the bad sectors have been mapped out at the factory.

Another advantage of regular formatting is better wear leveling performance.

The way flash memory cards (and USB flash drives) work is that the memory controller on the card assigns different areas of the card for specific directory locations each time the card is formatted. They do this for what is known as load balancing/wear leveling.

Flash memory has a limited number of write cycles it can tolerate before it fails. The number of write cycles each bit on a flash memory card can handle before it fails is very large but it will eventually wear out. So the controller tries to ensure that each storage location of the entire card is written to roughly the same number of times over the life of the card. What this means is that even after you format the card the controller will continue using parts of the card that have not yet been written to until each storage location on the entire card has been written to before it will go back and begin using the locations that have already been used.

Formatting regularly helps the memory controller on the card do a better job of wear leveling. If you leave the same files on half the card and repeatedly write files to the other half, erase them, and rewrite other files then all of the wear is going to go to only half the card and the life expectancy of the card before half of it fails will be shorter!

Formatting also allows for better card performance by increasing the likelihood of sequential write operations.

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  • Another good point! – Kai Mattern Mar 20 at 8:11
  • Formatting would help the memory controller if there was an interface to TRIM the SD card. But there appears to be no such command in the SD spec, so what formatting does is only making it possible to use more of the sectors. Now, if the card is FAT-formatted, most likely the camera's driver will write to the lower-LBA sectors first, and not touch the higher ones until necessary. To the SD card controller this will look as if the upper sectors are always filled, so formatting won't help wear levelling. – Ruslan Mar 24 at 6:49
  • @Ruslan Sector addresses are not static. The same sector address can be assigned to different physical locations by the SD card's controller. This is done precisely to enable wear leveling. TRIM has nothing to do with wear leveling, but is more akin to defragmentation of a hard disk. – Michael C Mar 25 at 0:43

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