Extremely slow speed when writing to USB FAT32 drive in Linux

I'm trying to copy around 4GB of files onto a USB 3.0 drive formatted with FAT32. The speed is ridiculously slow - 200 kBytes/sec. Writing data directly with dd is okay at about 25-30 MBytes/sec, and writing the same data on an ext4 partition on the same device is going at 9-10MBytes/sec. I am running Arch Linux at 4.1.2 kernel. Any ideas on what's going on?

The problem, as it turns out, was the sync option used to mount the filesystem, which appears to be performance-killer. Mounting it with flush option instead of sync solved the problem: sudo mount -o async,flush <device> <mountpoint>