Fusion drive unavailable after HD erase I wanted to erase the 3 TB Fusion HD on my iMac in order to install a clean system and start from scratch. The erase went fine except right at the end when it said something about core storage... (which I failed to capture, sorry)... and now the machine behaves as though the drive only sort of half exists.


There is no 'sub-disk' when I look with Disk Utility - i.e., there is no indented drive listed below "Macintosh HD"
The "Erase" tab is absent in Disk Utility
All partition options are greyed out in Disk Utility
I can boot in Recovery Mode, but I can't reinstall OS X because there is no drive available - it asks me to select a disk, but no disks are listed
diskutil sees the drive fine (screenshots below)


In case it's not clear from the images, distil cs list shows:

Logical Volume Group C970ADA-0D05-42AA-9E9C-403ED0E5335
Name: Macintosh HD
Status: Online
(3.1Tb)

    Physical Volume 7DAE3935-D0AD-42AE-AE2A-F6001F09187
    Index: 0
    Disk: disk0s2
    (120Gb)

    Physical Volume BA37C009-F93C-4EAF-9EF3-9C19772BD91C
    Index: 1
    Disk: disk1s2
    (3Tb)




diskutil list shows:
You probably deleted your Logical Volume and the superior  Logical Volume Family.

To create a new one boot to Recovery Mode, open Terminal and simply enter:

diskutil cs list #to get the lvgUUID (UUID of the Logical Volume Group)
diskutil cs createVolume lvgUUID type name size


or in your case:

diskutil cs createVolume C970ADA-0D05-42AA-9E9C-403ED0E5335 jhfs+ "Macintosh HD" 100%