Default [Q] Slow copying to micro sd card

I am using V30B Pure Repack by N00B and just bought a new micro sd card of kingston 16GB class 10.

I put the card into the phone, then connect the phone to PC via USB. I use mass storage mode. Then when I start copying file from PC to my phone, the speed only is 2MB/s write.

I wonder if it is a bad card.


I also did a benchmark and still got about 2MB/s write. I googled and had no clue.