Rockbox UMS - iPod Mounted with "sync" option
 ▻ time dd if=usb_write_test_file of=/mnt/ipod/Data/usb_write_test_file
4000+0 records in
4000+0 records out
2048000 bytes (2.0 MB) copied, 110.994 seconds, 18.5 kB/s

real    1m51.587s
user    0m0.004s
sys     0m0.232s

Rockbox UMS - iPod Mounted without "sync" option
 ▻ time dd if=usb_write_test_file of=/mnt/ipod/Data/usb_write_test_file
4000+0 records in
4000+0 records out
2048000 bytes (2.0 MB) copied, 0.0171083 seconds, 120 MB/s

real    0m0.103s
user    0m0.000s
sys     0m0.016s