Factors in SD read/write speed

I'm trying to figure out why my MicroSD card is being read, at what seems like, a slower than expected rate.

The card i'm using is the default 4GB card that comes with the Nifty Drive, that plugs into my SD card reader. It's a class 10 card and also has the UHS class 1 logo on, so I would imagine the minimum read (and/or?) write speed should be 10MB/s (correct me if I'm wrong please).

I'm using Blackmagic Disk Speed Test and getting speeds of around ~5MB/s.

Can anyone say why the speeds are ~50% less?

Just for comparison - I tried another class 10 SD card in the SD card reader on my Mac, and that reads at 21MB/s and writes at 14MB/s.

Think it may be that the MicroSD card isn't actually class 10 (even though its written on the card)?

Both tests have been performed several times under the same conditions - no other apps running, straight from reboot...

Think it may be that the MicroSD card isn't actually class 10 (even though its written on the card)?

Click to expand...

You're probably correct. I purchased a number of MicroSD cards on sale which supposedly were top of the line as far as speed goes. I wound up having to discard half of them. There are numerous counterfeit MicroSD cards and SD cards being sold as named brand cards. I'm not sure how one can tell them apart without wasting good money.

Thanks for the advice

Yeah, it's pretty hard to tell some counterfeit MicroSD cards and SD cards, but you can find some methods to track — if one has the time and knowledge.

Or just google… how to avoid counterfeit MicroSD cards and SD cards etc. and have a few looks:
https://www.google.ca/search?client...-8&oe=UTF-8&gfe_rd=cr&ei=fyhMVbTZIu7s8we1xIAw

The eBay seller has given me a refund after I pointed the slow speed out to him. Out of interest, I'm creating black files to see what size the card maxes out at, weather in fact it's 128GB (doubtful!).

I know now to stay away from eBay for storage.