I’ve now replaced this with another official Apple connectoer (like the Thunderbolt one). This was the set up before the problem:Īs you can see – the MyBook Duo is using a thunderbolt connecter which is pretty solid, and the WD Elements is using the USB hub connector, which sits quite loosely in the port, and can cause connetion (and hence power loss) if jiggled. My best guess is that it was the flimsy USB connector causing a power outage while writing (it wasn’t writing at the time – but maybe it was doing something under the hood). Not an ideal end to a couple of days of backing up, but at least I’ve got the disk back. After trying a few things – finding and killing a fsck process which had a handle on it worked for me: $ ps -ax | grep fsck $ sudo kill Īfter that – the disk became available again and I could Erase it in Disk Utility. A bit of googling revealed this was because some process had a hold of it possibly Spotlight, possibly something else. Then to unmount it: $ sudo diskutil unmountDisk /dev/disk1įorced unmount of disk failed at least one volume could not be unmounted The Fix On my machine the 4TB WD Elements was /dev/disk1.
Next step then was to force it to unmount from the command line. Unfortunately – Erase complained as it couldn’t unmount the disk in the first instance – just giving a ‘Couldn’t unmount disk’ message. I don’t mind losing the data – I just want a working drive back… Couldn’t Unmount Disk I tried a Verify, and then a Repair – which initially looked promising as it found a problem… but then it said it couldn’t repair and I should consider reformatting. Success! I could at least see the drive in Disk Utility now.
#COULDN T UNMOUNT DISK MAC MAC#
The next thing I tried was plugging the drive into an older Mac Book Air I have (which was running an older version of macOS). A bit more digging revealed the drive could be seen in System Report (via Apple logo on menu. The drive was still invisible to Finder and Disk Utilities.
#COULDN T UNMOUNT DISK MAC UPDATE#
So the first thing I did was update the OS (to High Sierra – as it turns out – a pretty substantial upgrade). A quick google revealed this wasn’t uncommon, and a couple of posts mentioned issues with Sierra. Whatever I did – I couldn’t get the new 4TB drive to show. Lights were on and flashing, but now they were not visible in Finder.Ĭue several attempts and unplugging, replugging, restarting the computer.
The connection was flimsy – so I figured they both just lost power and reset. I then plugged another WD Elements (an older 500GB one) into one of the other USB hub ports – and both drives disappeared from Finder. I could see the files on the drive – I even moved a couple of folders successfully on the new drive. When I got back from work it looked like it had finished ok. The 2TB transfer was left overnight and during the day. The MyBook Duo used the official Apple Thunderbolt adapter – which is pretty solid, and the WD Elements was plugged into a 3 port USB hub – which is a bit flimsy.
Its a 2017 model so has no native USB or Thunderbolt 2 ports – just USB-C, so I had to use adapters to plug in my drives. I formatted it and started with a 2TB backup of my 4TB (2x2TB RAID1 WD MyBook Duo). I recently bought a 4TB Western Digital Elements external drive in the Black Friday sales to add to add to my backup family. A tale of a brand new disk drive, a 2TB backup, a disk failure and finally a recovery…
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