how do I repair corruption and then erase everything on my external backup drive
My backup external drive has 6 partitions. I need to erase all and re allocate the space for new backups. Disk Utility will not unmount this drive, and First Aid 'found corruption that needs to be repaired'. How do I do this - presumably from Recovery????? H E L P! Please
Mac mini, macOS Sierra (10.12.6)