SD Card Speed test

While waiting for the GameShell to arrive I bought a new 32 GB Micro SD Card that qualifies for the new Application Performance Class (A1). This is especially geared toward installing apps in Android phones that are supposed to be as fast when installed to the SD card as when they are installed to the internal flash. There is also class A2, which is even faster, but only in sizes of 64 GB and more which is overkill for my GameShell.

While absolute read speeds don’t matter because the Gameshell’s internal SD reader is already maxed out, better random access performance has the potential for a big impact on booting Linux with many little tiny files. Or does it?

Here’s my readings, both with Image 0.21, extended via Gparted to full size. Stopped time from turning on up to display of launcher icons.

SanDisk Ultra 16 GB Class 10 HC I  SanDisk Extreme 32 GB U3 A1
33,7 seconds                       29,7 seconds
35,4 seconds                       29,0 seconds
30,1 seconds                       31,0 seconds

As you can see, it’s a bit inconclusive because of the one time the slower card booted in 30,1 seconds. What the heck? All in all, the faster card seems to shave of 3 to 5 seconds of boot time.

Recently for a project I tested sd cards speed on many single board computers and I was dissapointed and went with the usb drive option. Its a matter of sdio chipset and also this:


Basically, most SD cards are designed for photos and video where you are writing large files all at once (called sequential reading and writing). For ev3dev (and other embedded systems), we are much more interested in small files scattered around the file system (the 4k random read/write numbers). The manufactures don’t publish these numbers, so we have to do a benchmark to find out for ourselves.

As you can see from the charts above, the hdparm buffered and dd write numbers are roughly the same for all of the cards. This is not surprising since the advertised speed of most of the cards was about the same. These tests measure the sequential read and write speeds. But, where we can really see a difference is in the 4k random read and and write speeds.

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