how to copy all files USB SSD to my raid5 nas? (openmediavault 7.0.5-1 on debian(?))

sorry to ask stupidly simple question but i am noob on linux things. I have CM3588 NAS board and I have installed 4 SSD's and they are on raid 5 configuration. I have set up samba users.

I need to migrate all my files from my USB SSD drive to this new NAS, how to do it?

apparently I just attach this SSD drive to usb port of CM3588 and xcopy in terminal? but does that destroy raid 5 configuration?

help highly appreciated