UHS-II SD Card slower when read by non-UHS-II reader?

Started May 25, 2017 | Questions
jeffcarlson
jeffcarlson New Member • Posts: 1
UHS-II SD Card slower when read by non-UHS-II reader?

I need a sanity check, friends. I'm testing some USB-C SD card readers and have run into an odd result.

Testing read speeds from a SanDisk Extreme Pro 32 GB UHS-II/280 MB/s card, I get great results when I use the SanDisk Extreme Pro UHS-II USB-C Reader (the one Apple sells), because it reads the second row of pins on the card. Great.

However, when I put the same card into a reader that does not support UHS-II (i.e., it reads just from the first row of pins), I'm seeing speeds slower than when copying with a SanDisk Extreme Pro 64 GB SDXC/UHS I/95 MB/s card.

(I know the speeds listed on the cards are theoretical maximums; I'm mostly using those to differentiate the cards here.)

For example:

Copying 12.9 GB from UHS-II card (280 MB/s) via SanDisk UHS-II adapter: 01:06

Copying 12.9 GB from UHS-I card (95 MB/s) via SanDisk UHS-II adapter: 02:29

Copying 12.9 GB from UHS-II card (280 MB/s) via Cable Matters USB 3.1 reader: 04:55

I get similar results using other readers.

So the question is — thanks for reading this far — is it normal/expected that a higher-rated card should perform worse in most readers than a "slower" card? Is the UHS-II card taking away some throughput from the first row of pins in order to use the second row when using a compatible adapter?

Many thanks in advance for your nerdy help!

Jeff

ANSWER:
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hotdog321
hotdog321 Forum Pro • Posts: 20,884
Re: UHS-II SD Card slower when read by non-UHS-II reader?

I don't know if this helps, but when I updated to high speed UDMA 7 cards I found that most of my older readers wouldn't even read the card or worked dead slow. Even my Hoodman RAW Steel 3.0 performed poorly--until I contacted Hoodman and found a firmware update for the reader that fixed the issue.

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