recommended micro sd card ?

[hyperlogos]

If you want to be sure to get a useful test with pine, install Linux to the prospective cards and run the test in Linux on pine.

Thank you for that, hyperlogos; I know that is prudent advice, but I also know that do so far exceeds my capabilities.

It's no harder than installing android, you only have to install one package ("iobench") and run it on your boot device, you can for example run it in /home to get a good result.

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And a few months ago when I tested some Armbian Desktop builds for H3 boards (share the same SDIO implementation with Pine64) I was able to debug the dependency on fast random writes. If you open up something like Firefox for example then this app starts constantly writing to the card, uses fsync calls to ensure changes are written to card immediately and this alone blocks nearly all I/O when used with an 'average SD card'

Yes, it is common to disable fsync on devices with slow storage. This is done on many roms for the Transformer Prime, for example. I note that I actually get better performance with Linux on an SD card than I do in Android, and I blame it on Android's egregious overuse of fsync. We have a thing called delayed writes for a reason, and that reason is performance. You don't need to fsync several times a second unless your OS is so unstable that you expect it to explode any fraction of a second. But you do need to fsync more than not at all, so disabling it is not a solution either. Android desperately needs some IO scheduling work. I noticed this when downloading a file, too. You should NOT have any trouble downloading a file, because that's a stream, the system is doing little work, and Android should just cache the data until it has enough to be worth writing. That it doesn't is PATHETIC, and Android is exacerbating this problem due to bad design.