Yep, all consumers usually want is a bunch of numbers (presented as nice graphs of course) and ‘more is better’ or ‘less is better’ to avoid having to use their brain when making buying decisions.
But even those people deserve better since the average buyer of an SD card to be used in a SBC needs to be aware of a few pieces of information instead of staring only at graphs:
- Counterfeit flash memory is still a problem. Always ensure that you’re buying somewhere where a ‘no questions asked’ return/refund policy exists since it’s somewhat probable that you’ll end up with fake products (applies not only to SD cards but to all sorts of flash memory, SSDs included).
- As such product rankings of this sort are questionable by definition since even if the honest reviewer tested e.g. brand A to be the best, the person reading the review and deciding to base his own purchase decision on this might end up buying a fake A product. This actually happened and happens again and again: when for example Samsung entered the SD card market and countless reviews attested them to outperform their competition soon after the counterfeit crown went from Kingston to Samsung (the counterfeiters ofc printed the most popular logo on their fake products)
- Another problem is somewhat related: different production batches might perform differently and this applies especially to vendors who just buy whatever raw NAND flash available on the stock market to be combined with whatever FTL (flash translation layer) controller flying around. This affects all but a few manufacturers like Samsung, SanDisk, Kioxa (those have both knowledge and factories to produce their own flash and controllers) since all the others just do this: combine someone else’s flash chips + controllers and print your name on it (some like Kingston, Adata or Lexar then often ‘brand’ the controller firmware which identifies then as Kingston, Adata or Lexar even if it’s in reality a Phison, TI or Silicon Power controller). But even those vendors that produce their own NAND flash and their own controllers are affected by a similar effect: see my tests with SanDisk A1 and A2 rated cards from half a decade ago where the older and ‘lower’ specced A1 card outperformed the newer A2 card.
- Use case first! With the rootfs on an SD card almost all that matters is random I/O while sequential transfer speeds are (close to) irrelevant. Well, we all know that every consumer out there is trained to look at the wrong metrics… and that’s why it’s important to repeat this over and over again!
- Choose the right spec: over half a decade ago some of us did the painful job to test through various brands (me also starting with @geerlingguy’s iozone parameters just adding 16M block size since more appropriate) to measure which vendor currently provides the cards with highest random I/O. But fortunately that’s not necessary any more since SD Association defined Application Performance Classes A1 and A2.
So what an SD card buyer wanting to push this thing into any SBC really needs to know is only the following:
- forget about the brand but choose the seller wisely (‘no questions asked’ return/refund policy)
- choose A1 or A2 rated cards only (and if you’re also after higher sustained sequential transfer speeds then pay attention to the video ratings, e.g. choose something where next to the A1/A2 logo also a V30 logo is printed since such a card is not only fit for random I/O but has also to provide 30MB/s sustained write speeds)
- don’t trust in benchmarks somewhere on the net for these simple reasons: the card you’ll end up buying might be a counterfeit card or from a different batch (e.g. ‘Amazon Basics’ acquiring not only FTL controllers and flash from ‘SK Hynix’ but also from other vendors so your own card and the one from the reviewer have nothing in common except the logos printed onto the card’s surface.
- ALWAYS test the card you buy immediately! ALWAYS! That’s the only way to check for counterfeit flash products. With an SBC running Linux it’s as easy as using f3. 1st check with f3probe, if the card already fails with this return immediately to the seller. If this 1st check passes the 2nd check has to be made with f3write/f3read. This also tells you real sequential performance of the device you bought and is the only way to ensure you’ve not bought fake flash product.
And I guess that pretty much describes the dilemma: consumers love these lists of useless numbers presented as nice graphs, they look only at the irrelevant metrics and forget that the product they’re about to buy might have nothing in common with the one tested/benchmarked other than some logos. IMO these consumers would be better served by some educational sentences no-one likes to hear than those product listings 