Forum Revamp - Printable Version

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RE: Forum Revamp - tkaiser - 04-19-2016

(04-19-2016, 05:46 AM)rahlquist Wrote: Pine64' SDIO implementation (sequential transfer speeds max out at ~22/23 MB/s)
No point in going crazy and buying a 2,999X transfer rate card. If all you can let through if 5gallons per hour, there is no reason to have the city come out and hook up a 22" water main, you will never see any benefit.

But another performance factor is way more important since we're talking about SBCs here: random I/O

SD/TF cards were made for cameras/recorders. There sequential speed matters (how fast can large chunks of data written/read from card). When we're talking about SBC usage with Linux and Android that's mostly irrelevant since we're now talking about rather small chunks of data that are read/written from random locations.

Sequential transfer speeds are important for cameras/recorders and this is all what the 'speed class' is able to tell you: Card should be able to write/read large amounts of data sequentially.

But there is no such thing like 'speed class' when we're talking about the more important random I/O performance. And you can get two cards with exactly the same speed that vary here by factor 20-100. I post it one last time here: 

Cards that seem to perform identical when you look at absolutely irrelevant 1M sequential reads (that's what most card benchmarks measure -- irrelevant stuff for SBC useage) behave absolutely different when it's about small random writes/reads. And that's the main reason Android or a desktop Linux install feels slow like hell on one board and snappy on the other: random I/O makes the difference.

So when you have in mind that the rather cheap Samsung EVO with 32G or 64G do not show less sequential performance compared to more expensive cards, that they are able to exceed 21 MB/s when doing sequential writing (while they're just specified for 10 MB/s here), that they show superiour random I/O performance at this capacity (8GB and 16GB are slower here) and come with 10 years warranty then at least I know what to buy at the moment when we're talking about sequential transfer speeds limited to ~23 MB/s by the host.