Why is this happening? This has happened with any type of storage - HDD, SSD, and flash drives. Example: “Drive A” works fine with 1TB of data. Then, when hooking it back up, my lap top turns it into “MyBook” and EFI” with both partitions showing no data. Would doing a fresh reinstall of the OS and used programs help? If I were to plug the corrupted hard drives to another Mac that does not have this problem, will that computer have the problem too? Final question, would erasing the corrupted drives and creating new partitions fix them? Or should I just trash them and not risk anything? I already have backups and would like to be able to still use those hard drives again. I’ve heard possibilities of it being something with OS Sierra and the way it formats drives but then I’ve also read accounts of this same issue as far back as 2013. Some say it has something to do with Western Digital hard drives but that’s as far as it goes.