USB Rom Transfer - how do you know when it is complete?

[spud11]

Pi Model or other hardware: 3B
Power Supply used: Standard
RetroPie Version Used: 4.2
Built From: Pre made SD Image on RetroPie website and updated from source several times
USB Devices connected: 2x USB hubs; USB trackball; 2x homemade dials/spinners.
Controller used: 4 x USB DragonRise controllers
Error messages received: None

I've used the method found here: https://github.com/RetroPie/RetroPie-Setup/wiki/Running-ROMs-from-a-USB-drive
to transfer roms from a 128GB Sandisk microsd card to USB once before using the automatic method recently implemented in Retropie. I think this is one of the best recent features added to Retropie, by the way.

I'm now using this method once again at the moment.

I'm just wondering though if there is any way to check how far it has progressed. On that previous occasion, I just waited over night and hoped it had completed (which it had). (I recognise it's preferable not to have roms on the micro sd in the first place, but I don't mind waiting - I just want to make sure I know it's completed the transfer before switching the pi off.) Is there a way to check how far it has completed please eg by SSH? I can't find anything on the wiki that mentions this.

[scar]

@spud11 after loging in through ssh, you can use "du -sh <directory>" to check the size of the directory and can also use "ls <directory>" to see all the files that are in <directory>