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There seems to be a bug/conflict with internal platter drives greater than 4T ,  Mac OS 10.10.3 (Yosemite) , Disk Utility, and my souped up 2010 Mac hardware. When I bought a new 4T Toshiba drive, Disk Utility incorrectly formatted it to be a Logical Volume Group drive. This works, but I noticed it was wrong because it had no S.M.A.R.T. status, and couldn’t be used as a startup disk, which was my intended use (nightly backup clone of my OS using Carbon Copy Cloner.)  Also, once I unmounted it, there was no way to re-mount it.

The fix was to use Terminal to reformat the drive.

In Terminal, type:

diskutil cs delete “Put Your Logical Volume Group UUID Here”

Don’t know your UUID? Run Disk Utility’s “Verify Disk” on the problem drive and the UUID will come up in the notes.

Or, if that doesn’t show it, go to the Apple symbol in the upper left corner of the screen > About this Mac > System Report > Hardware – Storage.  Look for the LVG UUID (not LV, or PV or just UUID)

Be careful to use the correct UUID! This will erase and format the drive in an instant!  You’ve been warned!


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