Low perfomance when read from usb flash drive

[Artyom Mirgorodsky]

7.1 livefs test result:

 dd if=/dev/da0 of=/dev/null bs=65536
 19534+0 records in
 19534+0 records out
 1280180224 bytes transferred in 64.897932 secs (197263329 bytes/sec)
 
 systat -vm
 
 Disks    da0
 KB/t    64.00
 tps      301
 MB/s   18.84
 %busy     99