Backing up several 5Mo+ files from USB key to another one

I often have to backup between 500 and 1000 files each between 5 and 10Mo. The files are originally on an SD Card or a computer (SSD) and have to be copied to a USB key. So I need to copy USB to USB via the computer or SSD to USB. The issue I have is that it can sometimes take hours to copy all files if I'm using the computer at the same time. I would like to shorten that time as much as possible. The solutions I thought about are: 1/ bypass the computer by using an exteal device to copy from USB to USB (kind of a copier but for USB keys rather than paper) => Haven't found if such a device exist though... 2/ Make sure the copy process has a dedicated amount of resource from the computer to ensure constant speed => Haven't found a software with these functionality...

I wonder if someone has encounterd such an issue before and how he/she solved it. Thanks!

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