Reformatting fusion drive ?

[droplink]

HI

I have a problem with my fusion drive.
After numerous attempts to reorder the partitions and install / remove a windows partition (why is that never easy?) my hard drive is well borked.
I have effectively four partitions, but only one is visible.
The new Disk Utility in El Capital tells me two are present, (one 1TB, and one 100GB) but wont let me access the 100GB one, even after running a first aid.

So then, I have all my files backed up with TimeMachine, so no worries about zeroing the drive and reseting it completely. But how do I do this ? No such options are available in DiskUtility if I start up from the recovery mode ??

 

[marzer]

From the recovery partition open Terminal and use the command line to erase each disk:

diskutil eraseDisk {filesystem} {Name to use} /dev/{disk identifier}

Heres a good ref for using diskutil: http://www.theinstructional.com/guides/disk-management-from-the-command-line-part-1

Close Terminal, go into Disk Utility, assuming it was a Fusion drive installed at the factory, Disk Utility should notify you that it wants to repair the Fusion drive. The repair operation should restore it to a freshly partitioned fusion drive.