SD card speed differences

Question

I'm trying to benchmark a micro SD card, and in the process it seems that my laptop's card reader is to blame, but I would like to make more experiments to be sure of it.

I have a supposedly Class 10 micro SD card. I used dd to measure its sequential write speed, and even when varying block sizes, I never get over 9 MB/s, more often 7-8 MB/s. I suspected the card might be defective, but otherwise it is fine (all sectors are writable, no errors, etc.).

I installed and ran CrystalDiskMark via Wine, and got about the same speed, 8 MB/s. I then tried plugging the same card on another laptop and the card gets up to 15 MB/s. But this laptop uses Windows.

I searched a bit but found nothing mentioning whether the issue would be the laptop built-in reader, or the Linux drivers. What experiments could I do to obtain more information about it, e.g. check whether it's a driver issue, or a hardware limitation? I cannot install Linux on the Windows laptop (neither run it via a live CD), neither install Windows directly on the Linux laptop, but I can install and run any Linux software, or Wine-compatible Windows software, or run Windows through Virtualbox. But if I understand it correctly, all of these solutions would end up using the Linux drivers to access the card reader, so they would all be affected by the same issue, if the drivers are the cause.

Answer 1

I searched a bit but found nothing mentioning whether the issue would be the laptop built-in reader, or the Linux drivers. What experiments could I do to obtain more information about it.

It can be both, so try a few combinations. E.g:

• If the internal SDCard reader is connected via USB (not all USB is via external plugs) and all your USB drives max out around 9MB/sec then it will be a USB HW or USB driver issue.
• Or boot windows from a live CD (e.g. Hirens) on the linux laptop. Measure speed. If it is equally slow then once again it might be the hardware. If it is much faster then it could be the drivers.
• etc etc. Just build a matrix of potential causes and wipe it.

I cannot install Linux on the Windows laptop (neither run it via a live CD),

Why not? Live CDs (either via CD, pendrive or a even using a swapped HDD) usually work fine.

neither install Windows directly on the Linux laptop,

Can you boot a windows live CD on the linux laptop?

Wine-compatible Windows software, or run Windows through Virtualbox.

This will add additional layers and the result is likely slower.

But if I understand it correctly, all of these solutions would end up using the Linux drivers to access the card reader, so they would all be affected by the same issue, if the drivers are the cause.

Correct. The only way to avoid that is with a hardware pass-though device. Which means not using the SDcard at all from linux, and giving your VM direct access to it. This will not work with wine, but it can be done with the right software (e.g. vmware), the right CPU with support for it (AMD calls is AMD-V and Intel calls it VT-d).

Both need support from the BIOS which is often missing from a laptops BIOS.

Answer 2

Try running a benchmark on some other card,stopping the processes using your ram,clean up your system,and use an empty card and try to copy something from the drive which is more than half empty.If neither work maybe it's your ram and processor that might need some tweaks,try to run your laptop at turbo mode and leave most of ram and processor for copying process.It might be also that windows copying technique is different from linux as windows always leave file fragmented.Also if you had any other external card reader and 3.0 usb plug-in slot,try to use that.