If I were doing this, on linux or Mac, I would
How would one do this on Windows?
Asking for a scholarly friend.
Using Windows built-in RoboCopy utility is likely about as quick as possible. You can try using buffered disk I/O, which might (or might not) increase speed further for small files.
If all the drives are identical, it would be even faster to use a third-party tool to image one of the USB drives and then apply that image to all the other drives. These tools use direct disk I/O, without need to create a file structure and then to populate it, so the limiting factor is disk I/O speed, i.e., that of the USB drive and the HDD. On an old external HDD drive, using Macrium Reflect, I commonly see speeds of 80 to 100 MBytes/sec. Some free (for non-commercial purposes) disk imaging tools are Macrium Reflect, AOMEI Backupper and many alternatives. These are even more worthwhile tools in a commercial setting, and the cost is nominal considering losses of PC's that are not backed up.
The image method seems very sensible to me. It bypasses everything slow from NTFS data structures to virus scanners. It is also feasible on Windows.
There are quite a lot of RAM drive tools available, like ImDisk, it’s apparent successor Arsenal Image Mounter (never tried it) and OSFMount. You can use them to create an image. You can also use Windows’ native VHD image facilities to create an image, but then you must use a writing tool that understands it. They are available in Disk Management’s “Action” menu.
You can then use tools like Win32DiskImager or just Rufus to write the image to a USB flash drive or whatever. Rufus appears to also support VHD files.
