Random data read
The reason why we decided to test compressible vs random (and incompressible) data is demonstrated now. Not only are the read operations showing different performance values between compressible and incompressible data, it actually shows higher performance on random data than on compressible data!
On this test the Apple adapter comes again on top, but in this case by a significant margin, of around 10%. Again SDXC USB3 Reader comes in as last, this similar values as in the compressible data.
Random data write
Mimicking what usually happens on camera, shows some weird figures. To start with, it is slower than compressible data. This demonstrates that some kind of data compression is being performed by the SD controller. On the other hand, small block sizes makes all non Apple devices go awry, slowing down transfer speeds to a fraction. Although not common, this does shows the importance of mature implementations.
Finally, it’s amusing to see that the slower performance of SDXC USB3 Reader is still visible in cases it shouldn’t. 16 MiB/s is far shy of the 54 MiB/s bus limit of the device, which demonstrates how unoptimized it is.
Mixed random data
Random data is hard to compress and decompress, which means you’ll get a 1:1 ratio between write and read operation. This takes a heavy toll on the SD controllers, and on the readers.
Surprisingly again, Apple is defeated on the mixed test, and on one instance by a significant margin of more than 20%. Other than that, nothing relevant happens, SDXC USB3 Reader is still the slower reader.
Conclusion and final remarks
To start with, the Apple SD card reader. On average it’s the best overall solution. If you have one, don’t buy another reader, as you’ll be disappointed. If you need to read MicroSD cards, just get a passive adapter, which often comes for free.
All the tests show the effort takes to make sure it’s often the best performed on everything it does. Peak read and write performance is simply unbeatable. On the actual contenders, MicroSDXC USB3 reader wins hands down. It’s simply faster , and on most cases by a multiple. Peak performance is not as high or stable than on the Apple reader, but when comparing with SDXC USB3 Reader, there’s simply no comparison.
If you take into account that it’s also the cheaper and best form factor, you can’t be wrong by buying it.
If you absolutely need a full size SD Card reader, then go SDXC USB3 Reader, but be aware, performance will suffer, even on low performance SD cards.