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A2-class microSD cards offer no better performance for the Raspberry Pi

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Re: A2-class microSD cards offer no better performance for the Raspberry Pi

#111

Post by joshvm » Tue, Jul 23, 2019, 8:29 AM UTC

Vogtinator wrote: post #50

joshvm wrote: post #12

Earlier quoted context omitted.

SD card performance on the Pi Jeff's benchmarks are accurate in my experience. If you try saving single images from a camera at even 5-10fps, the card quickly bottleneck and you start dropping frames. If you buffer and store (in my case 16-bit raw), you can essentially saturate USB bandwidth if you're also using a USB camera.

No, the bandwidth isn't shared as both sd controllers (sdhci and sdhost) are directly accessible using MMIO (and DMA).

Thanks for clarifying that, I was never sure.

Re: A2-class microSD cards offer no better performance for the Raspberry Pi

#112

Post by Dylan16807 » Tue, Jul 23, 2019, 9:44 PM UTC

stefan_ wrote: post #2

Testing microSD card speed on a Mac is rather pointless because performance is (severely) limited on the Raspberry Pi through it's terribly slow interface, not necessarily the actual card. Remember RPi 1-3 use a plain SPI interface, and even the new 4 only has UHS-1.

Even at 25MBps, it's very easy to see if you're bottlenecked to less than a thousand 4K writes per second (4MBps), and pretty easy to see if you're bottlenecked to less than three thousand 4K reads per second (12MBps).

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