解决树莓派磁盘速度问题

外接磁盘绝对不能使用NTFS格式分区！速度非常慢
安装测试磁盘速度的软件： 
sudo apt-get install hdparm
测试本地card的读写速度：
hdparm -Tt /dev/mmcblk0

pi@raspberrypi ~/downloads $ sudo hdparm -Tt /dev/mmcblk0
/dev/mmcblk0:
Timing cached reads: 210 MB in 2.02 seconds = 104.21 MB/sec
Timing buffered disk reads: 54 MB in 3.09 seconds = 17.45 MB/sec
pi@raspberrypi ~/downloads $ dd count=50 bs=1M if=/dev/zero of=~/test.img
50+0 records in
50+0 records out
52428800 bytes (52 MB) copied, 1.55218 s, 33.8 MB/s

测试外接硬盘的读写速度：
hdparm -Tt /dev/sda1
pi@raspberrypi ~/downloads $ sudo hdparm -Tt /dev/sda1
/dev/sda1:
Timing cached reads: 316 MB in 2.01 seconds = 157.46 MB/sec
Timing buffered disk reads: 62 MB in 3.03 seconds = 20.48 MB/sec

pi@raspberrypi ~/downloads $ dd count=50 bs=1M if=/dev/zero of=/media/usbdisk/test.img
50+0 records in
50+0 records out
52428800 bytes (52 MB) copied, 13.5962 s, 3.9 MB/s

将external disk 格式化成ext4
sudo mount -t ext4 /dev/sda1 /media/usbdisk
pi@raspberrypi / $ sudo dd count=50 bs=1M if=/dev/zero of=/media/usbdisk/test.img
50+0 records in
50+0 records out
52428800 bytes (52 MB) copied, 1.15549 s, 45.4 MB/s

bingo!!