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Comment by meatmanek | Hacker News Reader

I'm surprised by the lack of mention of the A1/A2 "Application Performance Class"[1]. These classes specify minimum performance numbers for random reads and random writes: 1500/500 read/write for A1, 4000/2000 read/write for A2.

Notably, the Amazon link for the Sandisk Extreme points to an A1 version, not the A2 version[2]

  1. https://www.sdcard.org/developers/overview/application/index.html
  2. https://smile.amazon.com/gp/product/B07FCMBLV6

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My understanding is that A2 cards are generally slower than A1 cards IF you don't have host-side support for managing the volatile-RAM caching that A2 requires.

So if the Pi 4 only allows you to run in A1 mode anyway, you're better off buying the A1 card and both saving money and getting a faster card. I don't know if that lack of support is true of the Pi 4, but it does seem to be true of most other SBCs according to https://github.com/ThomasKaiser/Knowledge/blob/master/articl...

Ah, interesting, I did not realize there was a difference in protocol. I thought A1/A2 were just spec requirements.

I wonder if A2 support is something that could be added in newer kernels, or whether it requires hardware support.

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