In Pursuit of Micro SD-Card Speeds – Part 1

write-performanceWhen I recently read an article in a computer magazine about micro SD-card speeds in the range of 60+ megabytes per second I was quite amazed as my personal experience is an order of magnitude less. So I decided to get to the bottom of it and see if I could improve read/write performance.

Micro SD-cards are getting quite big these days. I mainly use Sandisk Ultra 16 GB cards these days as they feature a good mixture of price, amount of data they can store and the time it takes to clone a complete card, e.g. when I want to make an image of a Rasperry Pi SD-card installation. With a small USB-2 adapter I get read speeds of around 17 MB/s and write speeds of around 8.6 MB/s. These numbers are way below those given in the article for 32 GB Sandisk Ultra cards that achieve a read and write performance of well over 60 MB per second.

To get higher data rates a USB-3 capable SD-card reader is required. In a first attempt to get to higher speeds I bought a small USB-3 SD-card reader from UtechSmart. At a cost of 10 euros my expectations were limited and unfortunately, this proved to be right. The same micro SD-card in this reader could be read at 22 MB/s (up from 17 MB/s) and write speeds were at 13 MB/s (up from 8.6 MB/s with my USB-2 adapter). The screenshot at the top left of this post shows the difference between the same micro SD-card in the USB-2 and USB-3 reader. So while the graph looks nice the speeds I could reach with the USB-3 reader were still light-years away from the values in the test report.

So perhaps 32 GB cards are performing much better than the 16 GB cards I use? Or perhaps I need to get another USB-3 reader? Or perhaps the Linux driver for that reader is not optimized for higher speeds? It’s a bit of a mystery. But as the speed difference is significant, I will keep trying. Watch this space for part 2.