Class 10 slower than class 6

[stoopkid]

I just got a Class 10 16GB SanDisk card from NewEgg, upgraded from the same but Class 6. The Class 6 got up to 12.1 MB/s write but this Class 10 only gets up to 9.4 MB/s write. And it's consistently lower anyway. I'm testing with the benchmark on a 550D. I understand that the 550D should be able to manage around 20MB/s.

So what's the deal? Why on Earth might the class 10 card be slower?

[ItsMeLenny]

Maybe a dodgy card.

But also class numbers really mean nothing anymore.

[Walter Schulz]

Class specification is kind of outdated. "Class 10" should be able to write with (at least) 10 MByte/s. An UHS-I card would be a better choice.
It's not a crime to label a card with "Class 6" which is in fact able to do "Class 10".

On the label there has to be another number for transfer speed. Which one is given?

Ciao
Walter

[stoopkid]

It says "up to 30MB/s"... The thing is, it seems much faster in some cases. For instance formatting the card, even with low level seems way faster. And it seems faster on my computer. But the benchmarks and bitrate both perform worse on the class 10. Which is a bummer, it was on sale for only 10 bucks but I only got it to get higher bitrate.

[Walter Schulz]

Comparing performance for format operation doesn't make much sense.
Use a decent USB 3.0 card reader and CrystalDiskMark or ATTO. If your card doesn't give 30 MByte/s for sequential read it might be not an original Sandisk.

Ciao
Walter

[stoopkid]

I'm getting 20/10 RW with crystal disk. Looks like it came from a Marketplace seller on newegg, I'm gonna try to RMA it.