USB Drive Will Not Mount, Not Listed in Disk Utilities, but Found In System Profiler

I have a Seagate FreeAgent Go drive with the optional docking station. I use it to keep files that I don't access on a regular basis and as a place to do "quick backups" of things like my Paperless library or my Lightroom Catalog. This morning, I saw a message on my desktop (I didn't shut down) that I failed to eject it properly.

Now it will not mount.

If I run

diskutil list

it dosen't show up at all. It's not there. Period.

However, in system profiler, it shows up under the USB, but not under the storage.

Ok. So I thought my drive is dying. If I plug it into another computer, it works perfectly. In fact, I plugged it into a Surface RT of all things and I was able to read and write with no problem. It also works on another Mac (MBP 10.10.3) I go back to my iMac with 10.10.3 and nothing—it's like it dosen't exist.

Here's the kicker: I have another FreeAgent Go drive, exact same model and size as the one that dosen't work, and if I plug it in to the exact same dock, it works.

I have checked my console logs and the only thing that comes up when plug in the failed drive is the error message

USBMSC Identifier (non-unique): 0x00000000 0xbc2 0x2100 0x0, 2

I have removed all USB drives, did a warm reboot, a cold reboot and even a reboot in safe mode: no joy.

Everything I have searched for has something about not being able to boot and the fix is repairing the disk via recovery console. That's not my issue. I can boot just fine. I just can't read this USB HDD.

Anyone else run into this?

I just started having this exact same problem with my FreeAgent Go drive which has always been working perfectly. Like the original poster I cannot see the drive in Disk Utility but it does show up in System Information. After a little more digging I found that the OS is trying to repair the volume BEFORE letting Disk Utility see it via an process named "fsck_hfs". When I force quit that process in Activity Monitor (it's owned by Root so you'll need to give it permission), the volume immediately appeared in Disk Utility. I'm running a repair on it now - fingers crossed. My guess is that since this is formatted HFS+ Journaled something about the journal consistency got flagged and the OS is attempting to repair it from the journal. I'm shocked that they hide it from Disk Utility while it's happening though - much better would have been to display the drive there without mounting the partition, and display a message that this is being done. Oh well at least I can see why Windows would mount it but OSX won't now (any OSX machine would start performing the same repair process).

The problem was VirtualBox. Specifically, the Windows 7 VM instance I had running was "grabbing" the device for itself. So, it unmounted it from OS X and passed the USB port to the VM. It was doing it automatically so I couldn't see anything.

To fix, you uncheck the device next to the USB filter.

The filter automatically connects a USB device to the VM instance so you don't have to do it manually (like my Zune).

Now, this is where it becomes confusing...I have 4 VMs running and all are set to autoboot when the host (OS X) starts. I haven't changed the settings in any of those VMs in at least 2 months and the the Windows 7 machine in at least a year. I don't need to; as everything was working. Now, way back when I was configuring them, I did attach the USB drive to the VM so I could install programs, backup some files etc. But when I was done, they were disabled. Somehow, they got re-enabled.

For my case:

• The device doesn't show in Disk Utility
• It does show in System Information under USB
• It works in other computers
• Other USB sticks work in this computer
• Changing USB ports makes no difference

I just rebooted the system, then it's mounted and working correctly.