The internal storage on 3P2 is RAID (five SSD's striped) and will keep up with all 8 channels of recording (there aren't 10 channels of recording, but 8 recording inputs and 2 playback output for the 10 channels).
I'm personally not a fan of USB storage for long format recording. Despite the specs, USB storage never seem to keep up.
I've tried using 3PLAY with network storage (and NRS system). It worked, but there was a delay when you would start playback.