I'm trying to transfer about 20GB of music from my Arch Linux laptop to a Micro SD card, via a USB reader. The process starts off fine; the first ~50 songs take a combined one second, although from what I've read that's just to do with caching (or something...) and doesn't represent the actual speed. Then it goes to what I'd consider a reasonable speed, where each song takes anywhere between one and five seconds (the files are lossless, so maybe ~15mb on average).
However, after a few hundred songs, things just slow down completely. A single file will take about five minutes to transfer, and that's a conservative estimate. I left it running overnight and barely any progress had been made!
The card is a recently purchased class 10 Sandisk, and I've tried using it in both a USB and a regular SD card adapter, so I'd like to try some OS-level solutions before I investigate further into the physical side of things. I've also tried all three USB ports on my laptop and they all face the same issue. I've tried using the regular
cp -rv ~/music /mnt/sd command, as well as
rsync -rvh ~/music /mnt/sd, and the same thing happens with both. If, for testing purposes, I copy to a destination on the same partition then everything's fine, so it's definitely to do with it being on a different partition. I've also tried the suggestion posted here which didn't help.
My kernel version is 4.10.9.