HOWTO test SD cards and identify fake ones (mostly sold on ebay)
SD-cards, especially microSD cards, are very popular since they can store a lot of information in a very small package. They can be used by popular types of devices such as phones, tablets, notebooks and desktop PCs with a card reader. This makes selling fake cards that are reprogrammed to look larger than they actually are potentially very profitable.
Fake SD cards
SD cards are becoming rather cheap, especially the smaller-sized ones, but there is still a significant price difference between a 4GB card and a 64GB card. This makes it profitable to reprogram a 4 or 8 GB card to look like it's a 64 GB card when it is in fact not. Such fake cards are potentially found in both regular stores and web-stores, and they are especially common on e-pray (pray that you get something remotely resembling what you actually ordered). Getting a fake card seems to be more common than not on E-Bay.
How to test a SD card
f3[1] is a great tool for testing if your SD card is a fake or not. It comes with two handy command-line tools: f3write and f3read. The package is just named f3 on GNU/Linux distributions, so dnf -y install f3 or apt-get install f3 to get it.
Simply mount the fat filesystem and run f3write /run/media/your/disk/ and wait hours. Unmount the filesystem and eject the card and wait 2 minutes when it's done then plug it back in. Now mount the filesystem and run f3read /run/media/you/disk/ and it will test if the files that were written are read back correctly or not.
If the card is fake then f3read's output will look something like this:
SECTORS ok/corrupted/changed/overwritten Validating file 0001.fff ... 2097152/ 0/ 0/ 0 Validating file 0002.fff ... 2097152/ 0/ 0/ 0 Validating file 0003.fff ... 2097152/ 0/ 0/ 0 Validating file 0004.fff ... 2097152/ 0/ 0/ 0 Validating file 0005.fff ... 2097152/ 0/ 0/ 0 Validating file 0006.fff ... 2097152/ 0/ 0/ 0 Validating file 0007.fff ... 2097152/ 0/ 0/ 0 Validating file 0008.fff ... 1553440/ 543712/ 0/ 0 Validating file 0009.fff ... 0/ 2097152/ 0/ 0 Validating file 0010.fff ... 0/ 2097152/ 0/ 0 (...)
In this output some of the files are OK, they are fine, but starting above 7.6 GiB all the files are corrupted. The reason for this is that this particular card is presented to the OS as a 32 GB card but in reality it's only got 8 GB of flash. Data written beyond that is discarded or re-mapped depending on how the card is faked. On some cards, writing beyond its capacity will overwrite random previously-written files.
The output of a fake card in the image was sold by "FIVE STAR STORE" which operated under the aliasas "sseariver2009", "beautyzz2009" and "victoryduanshop" on e-bay.
Speed testing
If the card you got is real then you may want to test how fast it is. sdspeed is a good tool to do this. You can get it from https://github.com/flagsoft/sdspeed
What to do if the card is such fake
If the card turns out to be a fake and the real size is like 8GB then you can use fdisk(8) and create a filesystem on it by entering a size such as 15480000S which is slightly lower than the amount of sectors you would find on a normal 8GB SD card. You can use the "actual" size of a "fake" supposedly larger card, but you may not want to store important things on it long-term.
Alternatively use gparted and create a partition that is smaller than 8GB.
E-Prey sellers who are scammers and sell fake SD cards
- PAYPAL 孔岩 "*KONGYAN" using e-bay user "abigdealstore1"[2]
- PAYPAL "*FIVE STAR STORE" using e-bay user "sseariver2009"[3], "beautyzz2009"[4] and "victoryduanshop"[5]