If you ever tried using a microSD for your root or home filesystem on a small computing device or smartphone, you probably have noticed that microSD cards are in most cases a lot slower than integreted eMMC flash. Since most filesystems use 4k blocks, the random write/read performance using 4k blocks is what matters most in such scenarios. And while microSD cards don’t come close to internal flash in these disciplines, there are significant differences between the models.
Jeff Geerling [1,2] has already benchmarked the performance of various microSD cards on different models of the “blobby” Raspberry Pi. I had a number of different microSD cards at hand and I tried to replicate his results on my sample.
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Environment and tools
Just like Jeff, I used the open source (but non-free) tool “iozone”  in the current stable version that is available on Debian Jessie (3.429). Instead of using a Raspberry Pi, I used a cheap microSD/SD-USB2.0-adapter made by Logilink  connected to a desktop pc.
I disabled caches and benchmarked on raw devices to avoid measuring filesystem overhead. Therefore, I used the following call to
iozone to run the benchmarks (
/dev/sde is my sdcard):
$ iozone -e -I -a -s 100M -r 4k -r 512k -r 16M -i 0 -i 1 -i 2 -f /dev/sde
Benchmarked microSD cards and results
The following table provides the results I obtained (rounded to 10kb/s):
|Manufacturer||Make / model||Rating||Capacity||16M seq. read (MB/s)||16M seq. write (MB/s)||4K rand. read (MB/s)||4K rand. write (MB/s)|
Discussion, conclusion and future work
I can confirm Jeff’s results about microSD cards and would also recommend the Evo+ which has the best 4K random write performance of the sample. On the other hand, I am very disappointed about the Toshiba Exceria card. Actually running a device on this card with a very sluggish performance was the reason why I took this benchmark initiative. And indeed, after switching to the Evo+, the device feels much snappier now.
I think it would be interesting to add more cards to this benchmark (not only microSD but also regular SD cards and maybe also CF cards). Also, using fio instead of the non-free iozone might be interesting. Furthermore, doing the benchmarks internally on the device or using a faster USB 3.0 card reader might be also interesting.