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I'm using several SD Cards to continuously write data from different sensors on an embedded device. I noticed that all of them after some days have a couple of Mb which are not visible (even if the Show hidden files option is enabled)

not-empty-1

not-empty-1

After I format it it looks like this:

after-format

https://i.stack.imgur.com/I3NIJ.png

What could be the cause ?

Thank you.

ossx
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3 Answers3

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It seems that for some reason there are some broken files on the SD Card (created either by the embedded device or by Windows when the data files are removed)

Using chkdsk Drive: /F made the files visible and available for deletion.

[I would add a picture but I am not allowed as I don't have enough reputation]

ossx
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All file systems have some overhead. FAT32, NTFS, EXT, HFS, etc., all use some of the storage space in the drive for their own use.

Caturday Saint
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  • I understand this, but why is it different for each SD Card ? (I've had from several KB to hundreds of MB) – ossx Sep 02 '16 at 14:27
  • Different factors can contribute to the amount of space used. Assuming that you are formatting each card with the exact same format (such as EXFAT), then this is one less variable. However, if you leave them with the format that they came with, they could have slightly different variations (EXFAT, FAT32, etc.). Another issue is that the devices will count bytes differently, based on what their vendors decide. If you have the exact same size device from the same manufacturer, then you shouldn't have this issue, otherwise you might notice differences between two cards of the same size. – Caturday Saint Sep 02 '16 at 14:41
  • Also, if you are asking why a empty but not formatted card uses more: The more you use the card the more "Logging data" gets stored in the filesystem. The overhead the filesystem uses is not a fixed amount, it grows as needed. – Scott Chamberlain Sep 02 '16 at 14:41
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Format the usb then install this http://www.softpedia.com/get/System/Boot-Manager-Disk/Bootice.shtml and follow this fix

Worked for me.

Community
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Faisal
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