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I bought a 256GB MicroSD card from Walmart recently, branded as 'Onn' which I suppose is a Walmart generic brand. I was able to format it as ext4, and then I tried to rsync to the card — which froze and corrupted the card.

I've had this happen before, where rsync is apparently too fast for the card and it corrupts it. So I reformatted, copied over my files, then moved the card to my PinePhone (which runs Mobian, a Debian distro), and it won't auto-mount, and I can only manually mount it as read-only.

So, I bought a Samsung EVO 256GB card from eBay. As soon as I got it, I removed the existing partitions, created a big, ext4 partition, and as soon as it was done, it said the system didn't have permission to mount the partition.

After this, every attempt to mount, from Nautilus or the command line, resulted in variations on this error message:

wrong fs type, bad option, bad superblock on /dev/sdf1,
       missing codepage or helper program, or other error

I ran fdisk, fsck, e2fsck, and tried to repair the filesystem from the GUI. Nothing worked. The only think that worked was to run mkusb and restore the card to a standard storage device.

Here are my questions:

  1. The newer card shows up on my computer as 268GB, even though it's supposed to be a 256GB device. Is this a giveaway that it's a bootleg card? The packaging seemed legit and the seller was highly rated, but that seems suspicious to me.
  2. Is there an issue formatting an SD of this size as ext4? I have never heard of such a thing.
  3. Should I just leave the disk as FAT? I only use Linux for everything, so my impulse is to make everything ext4. I am going to put this disk in my PinePhone, and will be syncing to my server and to my computer, back-and-forth, and I have this idea that a FAT partition will store permissions differently and somehow complicate hte sync process. But that might be incorrect and it might just be standard to leave SD cards formatted the way they were purchased.

I'm running ubuntu 20.04.

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  • I updated the question to include my Ubuntu version. The questions kind of lean on each other, so answering one might resolve the others.
    – 3x5
    Jul 16, 2022 at 0:03
  • Have you tried formatting the card(s) exfat?
    – user68186
    Jul 16, 2022 at 0:05
  • Not explicitly — although I would assume it did format it this way, even though it says FAT32, because I thought FAT32 only went up to 32GB. Maybe it's FAT32+. Anyway, the card seems fine in its current format, but became unmountable as ext4.
    – 3x5
    Jul 16, 2022 at 0:18
  • Maybe try the f3 package to check the real card size.
    – ubfan1
    Jul 16, 2022 at 1:47

1 Answer 1

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OK, the answer to this question is that both cards were either fake, or low-quality.

  1. If your card's capacity is more than advertised, that's almost certainly a tell that it's a fake card.
  2. MicroSD cards can be formatted to Ext4 with no problem. However, you should remove journaling from the partition after you created it. You can do this by running tune2fs -O ^has_journal /dev/sdXY.
  3. There's no problem with an ext4 SD card. If you're strictly Linux on all devices, it's a bad idea to format as FAT or any of its variants. I found that if I put a FAT device in my computer, and copied over files using mc, the copying was much slower when the card was FAT. I also have some files with a question mark in the filename, and these cannot be copied to a FAT volume. So I wouldn't recommend it.

Using F3 (Fight Flash Fraud) was a good suggestion, and it did identify one of the two cards as fraudulent. I think the other one is just low-quality and I have read, anecdotally, that these Onn cards from Walmart are rebranded Sandisk cards that didn't pass Q/A. I'm not sure if that's true, but it does seem like the card was more fragile and reformatting it revealed this.

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