Hello Andy Jibb,
Welcome to Microsoft Community.
There may be several reasons for not being able to copy large files to a Windows storage space drive. Here are some solutions you can try:
1. Check disk errors.
Run a disk check utility to scan for any errors on the drive. Right-click on the drive, go to Properties--Tools--Error checking, and click on "Check". This will scan the drive for any errors and attempt to fix them.
2. Optimize the drive.
You can click on the previous step, in addition to "Check" another option "optimization", using this function can help you optimize the drive read and write speed, defragment space.
3. Check whether the file system is damaged.
If the file system on the drive is corrupted, it may cause problems when copying large files. You can try running the System File Checker utility to scan and repair any corrupt system files:
4. Update the driver and firmware.
Make sure your storage drive has the latest drivers and firmware. Check the manufacturer's website for available updates and install them accordingly.
5. Check the hard disk hardware.
If this is a plug-and-play type of detachable hard drive, remove it from your computer and send it to a professional hard drive inspection organization for inspection to confirm whether the hard drive has hardware faults.
Best regards,
Mitchell - | Microsoft community support expert from MSFT