@mitu My note about continuing to use related to my original post. So... Am I able to run the backup from the same pi that I'm using retropie on, whilst for example playing games at the same time?
What I'm wanting to avoid is having to use my windows laptop for the process as it's used for other things by the family and robocopy is so slow.
Ideally, I'd want to back up the ROMs on the usb directly to a network drive but all from within the pi (so that this can happen in the background and other life can carry on!)
I've managed to find some helpful tips for using rsync so will investigate those as well