We thought long and hard about this important subject.
The WD 4TB MyPassport Wireless Pro seemed ideal. Until you read the countless reviews of it malfunctioning or packing up completely. The concept is ideal for photographers in the field, but the execution was dreadful from such a top company. In the future, WD will hopefully get the problems corrected, but meanwhile that “ideal” option had to be ruled out.
Instead, we use two “normal” portable hard drives - a Seagate and Toshiba, both with good track records for reliability - making two copies of everything. The chances of both failing together are slim. Using two from the same company (and possibly the same manufacturing batch) would increase risk. A laptop provides the intermediary, as well as providing a great viewing screen. All of this data is eventually backed up even more securely back home.
Whether you’re a professional or serious amateur, caution is essential. “Be prepared” not only works, it’s underestimated as a practical key factor for success.
I come from the world of music and protools - and even back in using magnetic tape on 24 track machines - and we ALWAYS backed up 3 times. Triple backups or not at all. I have had, knock wood, only one time where I had to use my third copy in 40 years (magnetic tape - machine ate one, the second had a few rough spots). Hasn't happened on the hard drives but I have had some failed cards. Doesn't matter what u use, just copy copy copy!!!
I have a computer and backup drives at home.
I have 422GB of aerial work backed up just from 2017.
The OP was asking about a portable system.
The pic shows what I take when I go flying for a few hours -.
I agree that having too much footage on a single card is asking for trouble. However, I have been in many situations where I don't have the time to swap cards during every battery change. When the light is changing and the shot is about to go away it's nice to be able to keep the card in place. That being said, there are many situations where time isn't as critical and that practice is totally doable.
We calculated the cost of using many micro SD cards for an extended period of time away overseas and it simply doesn't compete with a reliable portable hard drive for bulk storage.
Like Meta4, we hardly ever record a whole flight - other than counting animals within a long stretch of river - as different from shorter planned sequences. But the amount of data nevertheless adds up when using 4K.
That said, if by "in the field" you mean just being away for a short time period, then micro SD cards are sufficient. And definitely swap them.