Disk util in recovery mode shows invalid disks - fixing merges the disks to a single LVG

Question

Seems another day, another interesting issue in Mac OS which has me stumped a little bit.
Background: My setup is the laster Mac Mini server, I have upgraded the root disk to a 256GB SSD and moved the ordered 1TB magnetic drive to the secondary disk.
I installed the system with Mac OS Mountain Lion and everything was fine. At this stage I had both disks encrypted with filevault. I then decided to play with some imaging and so destroyed the disks with diskutil cs delete UUID from the terminal in recovery mode (the installer would not work with the disks until I did this), at this stage everything is still ok and the system installed as expected. I then installed a second Mountain Lion instance to the secondary disk, and booted off this, to clone the SSD with disk util. Again, up until this point, everything is as expected.
Once I had the disk image created, I rebooted to recover mode, and attempted to clear the disks using diskutil and then reinstall Mountain Lion to the SSD, and have the magnetic disk as my users disk, at this point, disk util showed the disks in red. Clicking the disks, diskutil informed me that the disks were bad and I could either fix or ignore. If I ignored, then the installer could not use the disks, if i fixed them, then diskutil merged the disks into a single LVG of 1.25TB, which is obviously not what I wanted, no matter of permutations could fix this. I then had to open the terminal, destroy the LVG and then let the installer run (from memory, i might have had to create a default partition on the SSD before the installer could use the disk, but not 100% sure anymore (tried too many things!))
Now, when I open disk util in Mountain Lion, everything is fine, but if I reboot to the recovery partition, then the disks are in their invalid state still.
I found a macworld article (http://www.macworld.com/article/2015664/how-to-split-up-a-fusion-drive.html) which details pretty much what I'm seeing (see the quirks section), but I haven't got a fusion drive - I can only assume then that diskutil *thinks* I have a fusion drive!
- has anyone seen this before? is there a fix? can I make the disks valid in recovery-mode diskutil as its quite useful to partition the disks when installing the OS.
- does anyone know how I got into this state? is it because of two instances of ML?
- Is this a bug in diskutil? is it worth of a bug report?
As an aside, when running diskutil list in recovery mode, i see, from memory 13 disks (/dev/disk0 - 13) which seems strange, disks0 and 1 were my internal disk, disk 2 the ML net image, and then the rest were small, a couple of hundred K in most cases.
thanks!
SockThief

Answer 1

hey @keg55
brilliant! So I was mostly right now doesn't that make you feel good - to be honest, I'm gettingg rather sick of tools that are too smart and do what they think you meant, rather than what you **** well tell them!
It's was strange the timing of it, as diskutil (gui in recovery mode) only thought the disks were bad after I installed ML on the magnetic disk as well as the SSD.
So if I want to erase a disk (to ensure an absolute clean slate before reinstalling) is a diskutil eraseDisk diskX sufficient? I don't think writing 0's is really required, so zeroDisk/randomDisk/secureErase aren't really applicable to a simple reinstall. But, then I guess before installing, it will require a partition, correct?
I was thinking, perhaps I could solve this by making a 1:1 LVG, i.e.: put the SSD in an LVG and the magnetic disk in an LVG?