3 ms·
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 ran
by meatmanek 7y ago
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
- jack12 7y agoMy 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/articles/A1_and_A2_rated_SD_cards.md https://github.com/ThomasKaiser/Knowledge/blob/master/articl...
- meatmanek 7y agoAh, 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.