I'm thinking about making an unRAID box but the mover kinda mystifies me. I'll have a few tens of terabytes to dump on it initially, mostly from 4-8 Tb drives. I intend to plug them in with USB and transfer to the array. I'll be dumping similar amounts in the future.

If I only have a 500 Gb cache drive, can I only move 500Gb at a time before flushing the cache to the array? If I exceed its capacity, what happens? If a transfer is going on when the mover's scheduled operation starts, what happens?

I've seen people suggest I turn it off during large dumps. Is it dangerous to do so or can you just flick it off and on in the GUI without repercussions? And is the transfer worse (fragmentation?) for not using the cache, or just slower?