How to Connect a USB Flash Drive to iPad
苹果论坛：It's not officially supported,and you won't be able to copy any content back to the flash drive from the iPad,but there is this post which describes a work-around (and I haven't tried it) : https://discussions.apple.com/thread/3422226 . And if you are using a flash drive then generally they won't work with the camera connection kit - most of them need more power that is supplied to the iPad's port,so you'd probably be better off with a SD card if you really need to copy them on that way.
There are a number of apps that support DropBox,transfer from your computer via wifi,or you Could use email attachments - are they options that you Could use instead of connecting a flash drive ?
SD card 是推荐？
越狱行为，安装use driver,基本不用考虑：
You might have kNown that connecting external hard drive with iPad was made successful using Camera connection kit sometime ago. And Now the hackers found a way to connect a USB flash drive to iPad. This hack allows you to connect your flash drive with the iPad and via camera connection kit and browse,sync,transfer files,music,data using iFile feature.
Before you proceed,you must jailbreak your iPad using Spirit. You need to have iPad accessories that includes iPad camera connection kit (iKit) and install iFile (file browser) from Cydia.
Now when you connect your USB flash drive to your iPad via camera connection kit,your device might show an error that the device is not supported. Simply ignore the error message and open iFile on your iPad. You can Now browse all the contents available in the USB flash drive and sync or transfer data from iPad to USB flash drive.
As the iPad doesn't have a USB port I assume that you are using the camera connection kit (?). If so then you can only copy photos and videos to the Photos app with it - and even then they have to be in a particulat format
初步结论是official support is limited:
http://www.maclife.com/article/feature/seven_hidden_features_ipad_camera_connection_kit
