Unable to mount Time Machine partition

I have a WD external HDD which is plugged into my MacBook Air more or less all the time; it has two partitions one of which is my Time Machine disk. Just today I noticed that the hard drive is not mounting correctly anymore

• On boot-up, both partitions do not show up in the Finder at all

• When I unplug the drive and replug it back in, only the non-Time Machine partition shows up in Finder. It appears to work like normal i.e. reading and writing (I've already copied all my data off it)

• I can't seem to either eject the disk or unmount the partition that is mountable. If I hit the eject button in Finder, the partition name greys out and is not clickable but does not go away.

Via Disk Utility, I am unable to either mount the Time Machine partition (I get the generic not able to mount partition error message) and I am also unable to run Repair disk on it (error message: Disk Utility can’t repair this disk. Back up as many of your files as possible, reformat the disk, and restore your backed-up files.). Screenshot below. I tried erasing the disk but that also did not work (error message: Couldn’t unmount disk.)

It sounds like my hard drive has failed (or is in the process of failing) - the only things that I makes me second guess myself and make me wonder if the disk is salvageable are:

• The non-Time Machine partition appears to mount correctly and can be used as usual (although as mentioned above it cannot be unmounted)
• The drive is not that old all: probably about 18 months old. I have drives that are older that are still ticking along nicely.

Is this a simple case of a failed drive (perhaps a defective product) or is this a symptom of a software related problem (e.g. there have been several instances where the drive has been unplugged without being ejected correctly)?

Solution 1:

I had the same problem and resolved it like this.

1. Unplugged the drive
2. Turned off Time Machine in Pref
3. Rebooted the Mac
4. Plugged the drive back in
5. The Time Machine partition mounted

Solution 2:

I would guess it's most likely a logic corruption/error and not a physical corruption of the drive since the other partition seems unharmed. This has a chance of happening if you are writing/reading data and suddenly unplug your drive. Can't be 100% certain so if I were you I would definitely try to backup the other partition to another drive in case it fails as well.

(If you could post a picture of how the drive appears in Disk Utility it would be great!)

WD has a 3(?) year warranty (you can check the warranty status of your drive here) on HDD's that suddenly fail which would cover a manufacturing error.

Before going through the tedious RMA process I would try to:
1) Unplug the drive
2) Reboot the Mac (without the drive connected)
3) Connect the drive
4) Open Disk Utility again and try to repair/fix the partition
5) Run sudo diskutil verifyVolume /dev/diskN (where N is the volume name not the disk name) to try and see if the file system structure can be read at all.

6) Depending on the outcome of the command (it should return something like "the volume X appears to be ok" if it's fine) I would try to repair it with sudo diskutil repairVolume /dev/diskN

7) As a last resort, run sudo diskutil eraseDisk {Format} {NewName} /dev/diskN (replace {Format} and {NewName} with your preferred file system and new name for the drive) which will try to erase the disk and apply a new file system. This will remove your previous partitions and you will lose the data on the disk.

If I'm being stubborn I would try to find a good disk repair software and run that to diagnose the drive before doing the RMA-process.