Continuing the discussion from Librem 6 Look Ahead Wishlist:
and @WinstonSmith
Edits
- Clarify that cellular modem kill switch was used to disable the modem prior to testing. This matters because the cellular modem is on the same USB bus as the card reader.
- Add separate test data for desktop using a USB 2.0 port.
- Add some information about the spec of card that was used.
/Edits
That is my opinion too.
OK, so I have shut down my Librem 5 and removed the µSD card and booted phone. I have then tested said card in a USB 3.0 card reader dongle.
write speed tested with dd if=/dev/zero of=test bs=1M count=1024 conv=fdatasync
read speed tested with dd if=test iflag=direct of=/dev/null bs=1M
so I am testing with files that are 1,073,741,824 bytes in size i.e. 1 GiB.
from middle-of-the-road desktop
(dongle plugged into USB 2.0 port)
W: 21.5 MB/s R: 39.5 MB/s
(dongle plugged into USB 3.0 port)
W: 37.7 MB/s R: 87.7 MB/s
(dongle plugged into USB-C port of phone)
W: 33.9 MB/s R: 73.8 MB/s
So we can say that the combination of card reader and card is certainly not setting the world on fire and also not going anywhere near the USB 3.0 bus speed, and Librem 5 performance is reasonably close to desktop performance - so very likely the card or card reader is the limiting factor. But at least we know what the card is capable of.
Now shut down the phone and install the µSD card in the internal card reader and boot phone.
(using internal card reader of phone)
W: 12.3 MB/s R: 10.8 MB/s
You will note that the speed is much much less when using the internal card reader, as compared with using the USB-C port with a dongle, and way way below USB 2.0 bus speed. When reading, the card would be capable of using all of the USB 2.0 bus speed but it doesn’t get anywhere near it.
Why is it so?
Maybe @WinstonSmith would like to repeat at least the last part of that.
My card is a SanDisk Ultra. It is labelled as being able to use the UHS-I bus protocol (not higher).
It is labelled with speed classes C10 and U1. However the testing above tentatively suggests that it is actually capable of U3 speeds when in a suitable card reader.