Realistic SD card speeds

[DDY]

It is normal for a card that's sold as class 10, UHS class 1, to have sequential write speeds of just 7.5MB/s?

I was expecting a something closer to 10MB/s, i.e. Class 10 performance. Or, is it common practice for memory card manufactures to over exaggerate their product's capabilities by that much?

The product in question is a brand new Sandisk Ultra 32GB Micro SDHC card, the only other class 10 card I have manages 9.5MB/s seq. write which IMO is much more reasonable.

Have I got a duff card? How fast are your class 10 cards?

[Kumagoro]

Does the class apply to writes, I think I have read abefore that it only applies to reads... it could be that I just remember wrong though.

[DDY]

Does the class apply to writes, I think I have read abefore that it only applies to reads... it could be that I just remember wrong though.

Applies to both according to Wikipedia;

Speed Class Rating
The SD Association defines standard speed classes indicating minimum performance to record video. Both read and write speeds must exceed the specified value

[Funkstar]

What card reader are you using?

That can be a huge limiting factor. I've used a Lexar Professional USB2 SD/CF card reader for a few years now. It max's out at about 25MB/sec on Sandisk Extreme cards. Would like to get a USB3 expansion card for my PC and the USB3 version, copying from 8 or 16GB cards can be annoyingly slow (it's not actually slow, just my expectations have shifted overthe years )

[kalniel]

As above, check the reader and USB port.

My Sandisk Ultra 32GB SDHC class 10 UHS-1 card manages at least 40MB/s write speed (it's rated at 45MB/s and according to Windows transfer rates I hit that most of the time). I have the USB 3 version of the lexar card reader. It seems astonishingly quick.

It's not a micro one though, so probably not comparable - what speed is yours rated at (SanDisk usually give a read/write speed on the packaging)

[TheAnimus]

Where are you buying the cards from? There are a lot of fakes, some just have less capacity, some lack the speeds.

[DDY]

I have a strong suspicion it might be a dodgy card, it was the cheapest Sandisk Ultra 32GB I could find on ebay! The seller had sold thousands and had lots of positive feedback, still, wouldn't surprise me if it's counterfeit.

The card is rated class 10 and UHS class 1, on the packaging it states "up to 30MB/s". I benched the cards through a few cameras via USB and the on-board SD reader on my Dell, I'm suspicious because the cheaper class 10 card I have consistently outperforms the Sandisk on all readers by about the same amount.

[Funkstar]

...cheapest... on ebay!

Uh-oh......

[watercooled]

Yeah Class x should refer to the write speed too, as that's generally an important metric when choosing a card for a camera so it can keep up, especially with video. See if you can find any reviews of your card online to compare. Sandisk cards tend to meet or exceed spec in my experience, I can't say the same for Kingston though...

Random speed is often not great , so you'd have to find some reviews to get an idea of performance in that area if it's important. I think that's why some phone manufacturers discourage the use of microSD cards, as they have the potential to negatively impact user experience. In fact, higher class cards often perform worse here than cheaper ones.

[Domestic_Ginger]

I have class 4; slow like snail.

The speed is usually the write speed as far as I know.

[DDY]

I sent the card back to the seller who refunded me in full, although confident the card is genuine.

The seller might be telling the truth, after more digging I've come across a few user benches, all of which had sequential write speeds of around 8MB/s, it may well be Sandisk who's over-exaggerated the capabilities of the card. Even so, I'd still want my money back.

[kalniel]

it may well be Sandisk who's over-exaggerated the capabilities of the card.

That'd be unusual in my experience of Sandisk cards. I've got three different ones of various ages and technologies and they've all been dead-on the rated speeds, provided you have the backend to allow them to.

[watercooled]

Likewise, I don't recall any Sandisk SD cards which have performed below spec.

Some of their cheaper flash drives are, well, cheap. But they don't claim anything else.

[mattzaboss]

maybe its your reader, borrow someone elses card and check