I have here a 64GB Micro SDHC card. It is not labelled as SDXC, its manufacturer has quite clearly labelled it as SDHC. While this is not my supplier, the image at http://www.militarygrade.org/blog/2014/06/military-certified-compact-portable-memory-new-64gb-micro-sd-microsdhc-class-10-tf-flash-card/ appears to be of the same card.

I am attempting to install Linux onto the card. I am using a standard USB SDHC-compatible card adapter to access it. It is correctly reported as having approx 63GiB capacity. I have repartitioned it with two 31.5GiB partitions, but for some reason whatever I put onto the second partition doesn't seem to work. If I put an ext4 filesystem on it, it isn't recognised when I try to mount it. If I put a fat32 filesystem on it, the filesystem seems to work ok, but any files I store on it disappear if I remove and reinsert the card.

I initially assumed that the card was actually an SDXC card and my SDHC reader was unable to access anything beyond 32GB on it, but running badblocks -w on it didn't report any errors so I don't think this is the actual fault.

Any other suggestions as to what might be going on?

Edit: The plot thickens

So, doing some additional experiments I decided to partition the device as if it had a capacity of 32GiB. And it still turns out that the second partition doesn't work properly. By writing a pattern to the device using dd, removing and reinserting it, and testing individual sectors, it seems that every sector from 16785192 onwards (shortly above the 8GiB point) simply does not store data sent to it. I'm a little surprised that a device should fail in this way, but I can't see any other logical explanation for it at this time. So unless anyone has other suggestions, I'm inclined to put this down to hardware failure.

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    If it's a nonstandard card, you may well be out of luck. SDHC only goes up to 32 GB. – Daniel B Oct 1 '14 at 4:50
  • I was afraid of that, but I'm still perplexed as to why badblocks -w doesn't find anything wrong with it. It can clearly write data and then read it back, so why doesn't putting an actual filesystem on it work? – Periata Breatta Oct 1 '14 at 8:01
  • Your edit makes it clear you have a fake. They report a capacity higher than they really have, once you write beyond their real capacity you lose your data. You have an 8gb SDHC card that's been tampered with to report 64gb. – Loren Pechtel Oct 23 '14 at 22:12

Seeing that you got 64GB for only 12.99$, plus a case and a card reader can only make me think about a fake uSD card. For this price you should only have a 32GB, without anything and barely class 4 uSDHC.

Plus mil-spec stuff are generally much more expensive since there is certification price included in it. And, they don't even say what kind of resistance that uSDHC has, like electromagnetic, water/dustproof, etc.

I mean, even some non mil-spec/consumer uSDs like Samsung's are certified against theses hazards.

Sorry for you man. :(

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    That’s right. If data simply disappears, it’s not a failure, but fraud. I suggest you contact the dealer and demand a replacement or refund. – Daniel B Oct 2 '14 at 8:13
  • Just for the sake of clarity, I didn't purchase the card from that vendor, and actually paid quite a lot more for it than is described there. But the card does appear visually identical to the one they show, which is why I linked it. And you're right, the performance I'm getting from it is nothing like a class 10 should be... – Periata Breatta Oct 4 '14 at 23:59
  • in actual fact, I'm only getting about 2MB/s writes in ideal circumstances (4MB blocks, single threaded, no fragmentation). – Periata Breatta Oct 5 '14 at 0:19
  • Unfortunately, it confirms what I thought, 2MB/s in the ideal conditions is very very slow. :( You should really try to have a refund. – X.LINK Oct 10 '14 at 2:32

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