FakeFlashTest fails my 64GB Micro SD cards, but they work fine

I am hoping someone might understand what’s going on here and be able to explain to me if my cards are fine or not.

I recently bought two 64gb micro sd cards (SanDisk Ultra) from Ebay, the seller’s called ‘atmemory’, he has an excellent rating & many sales. I’ve even bought from this seller before without issues.

I always like to test my sd cards before I put them to use, so I run FakeFlashTest, H2testw & CrystalDiskMark to benchmark them.

Well FakeFlashTest reports this
BAD MEMORY from sector 107859 (52.0MiB) to sector 77624659 (37,902.0Mib)

I get a similar message from the other card, only from 1000’ishMiB to 37,902.0MiB.

The thing is though, both cards pass h2testw with a write speed of 40MB/s & read speed of 80MB/s for the entire 64gb of storage.

CrystalDiskMark benchmarks results are also great, except for one of the cards that has extremely bad random 4k writes, like 0.008 MB/s. Those results look like this: http://imgur.com/IjUOhOf

I’ve also tried loading them up with 64gb worth of media and all the media seems to work fine.

So the cards work fine, the read/write performance is good too, except for bad 4K writes on one of them. So what’s going on with FakeFlashTest? Is the message a false positive or is there something fishy about my cards? Anyone got a clue?

I have tried to google the ‘problem’ hoping to find similar cases, but no luck there.


One other thing, when I run FakeFlashTest and it writes the ‘Marker Blocks’ this is done extremely fast on my previous cards, like a few secs per block, but on these new cards it takes a long time and looks like this: 

Slow Writing marker blocks

And on my previous card that report nothing it’s fast and looks like this:

Fast Writing Marker Blocks

If H2testW is not showing any lost data and you can copy 64GB of data and read it the cards seem to be genuine. I am not familiar with Fakeflashtest but if it is only looking for bad blocks the test is flawed. All flash memory will have some amount of bad blocks. This is the nature of flash and is why there is a reserve space in all flash memory products. 

Yeah, I’m not going to pretend I have a deep understanding on how FakeFlashTest works, so that’s why I was wondering if this might be a false positive.

Here is an article about the program.

That said, I’ve never had it fail on any of my micro sd cards before.

What about the crappy 4k random writes on one of my new cards, is that not unusual?

Thanks for the reply, I will investigate further.

micro sd cards are mostly designed for the use in cell phones or action cameras where throughput is mostly sequential and large files. 4K speed are almost always really slow for this type of product. The sequential speed test is showing the correct speed. If the card was fake it would not meet the advertised speed. that said the speed advertised is sequential and there is no defined speed for 4k random writes. This is pretty typical for this type of product. if you are interested in 4k random write speed you would need to look at a SSD type product. 

Yeah I agree. If the card was fake, the read/write speeds would probably be terrible all over and it’s functioning size would not be 64gb.

I will put these to use and see how they work.