Usually, if you can't copy files to an external hard drive on a Mac, the drive is probably set with read-only permission, NTFS formatted, or corrupted. Your posted information shows that your Toshiba external hard drive has some file system errors but is still accessible.
Just as First Aid suggests "Mac OS can't repair disk. You can open or copy files on disk but can't save changes to files on disk. Back up on disk and reform it as soon as you can", you need to rescue the files on the external hard drive as soon as possible and then format the drive to fix it.
However, if your disk is inaccessible and corrupted, you can't copy files from the external hard drive to your Mac, in this case, you have no choice but to use a data recovery tool like iBoysoft Data Recovery for Mac to recover files from the corrupted hard drive first.
Then, you can feel relaxed to format the external hard drive on your Mac. By the way, if you want to fix the corrupted external hard drive on Mac without formatting, you can also try these ways:
- Check the IDE / SATA USB Connections
- Repair external hard drive with FSCK command
