有个500G的移动硬盘，直接插到pi上直接没反应，百度后发现是电源供电不足，再买个USB HUB。
问题来了，HUB一接上电源，pi就自动挂了，ping不通，电源灯还亮。
官网解释：
2. CAN I POWER THE RASPBERRY PI FROM A USB HUB?
It depends on the hub. Some hubs comply with the USB 2.0 Standard and only provide 500mA per port, which may not be enough to power your Raspberry Pi. Other hubs view the USB standards more like guidelines, and will provide as
much power as you want out each port. Please also be aware that some hubs have been known to “backfeed” the Raspberry Pi. This means that the hubs will power the Raspberry Pi through its USB cable input cable, without the need for a separate micro-USB power
cable, and bypass the voltage protection. If you are using a hub that “backfeeds” to the Raspberry Pi and the hub experiences a power surge, your Raspberry Pi could potentially be damaged
再在网上搜了一些，有一个案例，HUB上插移动硬盘，鼠标，键盘等USB设备，移动硬盘就带动不了了，拔下一些就好了
结合我的pi情况，是不是多插一些就好了，或者调整下顺序，先对移动硬盘供电，再backfeed我的pi，这样影响会不会小点。
于是把移动硬盘插到离HUB供电口最近的一个口，连pi的接到最远的一个口，本来还想中间再接一些东西，但这时pi也能正常稳定启动，移动硬盘也挂载了。
pi本来当电子玩具玩的，没想过稳定性要多久，能用就行
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