I recently bought several new SD cards. Two 32 GB cards and a 128 GB card, all Sandisk Extreme, class 10, 45MB/sec. (Yes, that is Bytes not bits). Although I had bought from Amazon itself (not Amazon Marketplace, let alone Ebay), I decided to run some proper tests to make sure that they were not fake, and also that they worked perfectly, and at the advertised speed.
Fake cards are programmed to report incorrect "upgraded" sizes, so a 1GB card that failed testing might be sold as a 16GB card. If formatted in the camera it will still show 16GB and will appear to work, at first. Obviously if you keep writing data to it, your photos will go into a black hole from which they can never be retrieved.
I used this software:
http://www.heise.de/download/h2testw.html
It is rather slow but very thorough. It writes different data each time so it can spot if the incorrect data is retrieved. If you have any concerns about your cards, run this test. To work it, first delete every file and folder on the card. Note what drive letter it shows up as. Click on English unless you are German. Select the correct drive, then Write and Verify. If it is a large card, allow a few hours, perhaps leave it running overnight. (Afterwards format the card in the camera - the program leaves it full.)
The program sometimes reported that my cards were faulty. I eventually pinned it down to a type of USB3 extension cable. (With an old USB2 reader attached to my laptop, all was well.) I use USpeed and Anker USB3 readers that work with all card types. I have multiple USB3 extension cables for my PC which is on the floor. I have had problems before with a particular type of USB3 extension cable and had returned some, and had thrown away some. But I had continued to use the cables that appeared to work. I now found that was a mistake and I have thrown all my cables of that type away. I also have Startech.com USB3 extension cables and they do work correctly.
So everything now works perfectly. If I had not checked this, sooner or later I would have had corrupted photos, and would not have known whether to blame the camera, the card, the reader, the cable or the computer.
Fake cards are programmed to report incorrect "upgraded" sizes, so a 1GB card that failed testing might be sold as a 16GB card. If formatted in the camera it will still show 16GB and will appear to work, at first. Obviously if you keep writing data to it, your photos will go into a black hole from which they can never be retrieved.
I used this software:
http://www.heise.de/download/h2testw.html
It is rather slow but very thorough. It writes different data each time so it can spot if the incorrect data is retrieved. If you have any concerns about your cards, run this test. To work it, first delete every file and folder on the card. Note what drive letter it shows up as. Click on English unless you are German. Select the correct drive, then Write and Verify. If it is a large card, allow a few hours, perhaps leave it running overnight. (Afterwards format the card in the camera - the program leaves it full.)
The program sometimes reported that my cards were faulty. I eventually pinned it down to a type of USB3 extension cable. (With an old USB2 reader attached to my laptop, all was well.) I use USpeed and Anker USB3 readers that work with all card types. I have multiple USB3 extension cables for my PC which is on the floor. I have had problems before with a particular type of USB3 extension cable and had returned some, and had thrown away some. But I had continued to use the cables that appeared to work. I now found that was a mistake and I have thrown all my cables of that type away. I also have Startech.com USB3 extension cables and they do work correctly.
So everything now works perfectly. If I had not checked this, sooner or later I would have had corrupted photos, and would not have known whether to blame the camera, the card, the reader, the cable or the computer.
