Check what type of partition table you are using MBR vs GPT.

Compare the power settings between both computers, it may be set to different polling times for usb / hard drives.

Cant hurt to check what crystal disk info says while you are at it.

I am not saying what is best, but other options would be a software raid like (newer) Windows storage spaces and (older) dynamic disks, on Linux LVM, is similar; if it is only a two-disk array, you can even get a cheap or not cheap raid card, or even less dependent is have 1 be a continuous sync to the other. (This would have the most performance downside, but the pro is it will have the smallest stack of technology when accessing the data on new hardware.

Also, you can cache the movie in a RAM-disk, just the latest movie.

Maybe you need multiple servers to handle the demand with a load balancer.