Mobile Storage Devices Compatible with Apple iDevices
There are a few special storage devices for mobile devices. There are portable, bulit-in WiFi hotspot hard drives for mobile devices made by Western Digital and Seagate.
You need to install and use the mobile device maker’s iOS App, in this entire list, to take advantage of all these mobile storage drive features.
http://www.wdc.com/en/products/products.aspx?id=1330
http://www.wdc.com/en/products/products.aspx?id=1660
https://www.seagate.com/consumer/backup/wireless-plus/#features
There are special mobile lightning connected and built in WiFi Hot spot, USB flash drives made by SanDisk (now owned by Western Digital)
https://www.sandisk.com/home/mobile-device-storage/ixpand
https://www.sandisk.com/home/mobile-device-storage/ixpand-mini
https://www.sandisk.com/home/mobile-device-storage/connect-wireless-stick
http://www.adamelements.com/iKlips/iklips.html
This listing maybe incomplete and somewhat outdated, now. So do an online search for similar external data storage devices for iPads
Kingston Electronics makes some data storage devices for iPads/iDevices, now, too!
https://www.kingstongo.com/us/usb/datatraveler-bolt-duo-flash-drive-for-iphone
Someone mentioned, just recently, using on one these with an iPad that uses a wired Lightning cable from drive to iPad for faster data transfers of photos and videos.
LaCie DJI Copilot BOSS LACSTGU2000400 Computer-Free in-Field Direct Backup 2TB Rugged Hard Drive and Power Bank with SD Reader - with 2X Polaroid 8GB MicroSD Card, Memory Wallet
Direct LaCie Website link to drive below
https://www.lacie.com/products/dji-copilot/
Amazon link to same drive below.
Good Luck!