Can't Unmount External HDD

[CrazedVW]

I've got a 2TB Seagate external desktop Backup Plus drive divided into three partitions (My backup, Wife's Backup, and a third for large files that need to be transferred between machines), all formatted as Mac OS Extended that I can no longer do anything with.

A couple weeks ago one of My Backup refused to mount. Even in disk utility it won't mount. I tried running first aid on it - running Verify Disk says it needs to be repaired but running Repair Disk gives an error message that it can't repair the the disk.

I went ahead and bought a new external drive for back up so I'm no longer concerned about any of the data on there.
When I try to erase the partition that won't mount Disk Utility gives me an error message that it "Couldn't Open Disk". When I try to erase the disk it gives me an error on the other two partitions that it can't unmount. Same thing for when I try to repartition the drive. I've gone into Terminal and told it to force unmount the other two partitions but it still doesn't allow me to erase the disk. I also booted into recovery mode and tried disk utility from there but received the same error messages. On top of all of that I've tried these steps on several other Macs and get the same results. I also tried connecting it to a PC but I guess because the partitions are all formatted for Mac OS Extended none of them are recognized.

Any ideas? I'd like to recover the drive and make it usable again but everything I've found through searching so far seems to not be working in my case.

 

[Fishrrman]

A suggestion:
(Note: this can work ONLY if there is NOTHING on the entire drive (all partitions) that you need to save)

Take the drive to a PC, and re-initialize the entire drive, into one PC-formatted partition.

If this works, take it back to the Mac, and now see if Disk Utility will re-initialize it back to HFS+, journaling enabled.

If DU is able to do this, run the "Repair Disk" option on the drive about 5 or 6 times in succession.

If you get a "good report" each time, I'd consider the drive usable again...

 

[CrazedVW]

Thank you for that. I went to plug it in and do what you said through Windows in Parallels and for whatever reason the drive decided to mount as normal and I was able to reformat it the normal way through Disk Utility. First time it's worked correctly in almost two weeks. Ran the Repair Disk and everything seems to check out fine. Very odd.

 

[ColdCase]

I Had something like this happen when, I think, the disk was unplugged when one of the time machines was backing up. Some flag got set that TM was still using the partition/drive and, well it wouldn't mount, dismount, repair..... I forget what I ended up doing, perhaps ran TM backup to its conclusion again, but it eventually worked fine, just as yours did.