"Free Space" Partition disaster on new Mountain Lion iMac

You might want to take a look a the man page for diskutil (the command line version) for the options to manipulate coreStorage.

In addition if you search for things like logical volume and/or fusion drives you'll see that a Logical volume cannot be manipulated like a native drive can. I think you'll need to contact Apple and find out just want the drive should look like.

Ok I'll try this one more time. From your first screen shot:

You're system is configured with a Logical Volume Group. The underlying physical disks in a LVG cannot be directly manipulated.

A logical volume group is part of Apple's Core Storage Technology. CST has been around for a while in the OS but has just recently come to prominence because of the introduction of the 2012 iMacs and Mac Minis and Fusion Drives. Logical Volumes is how the SSD and HD are combined into a Fusion Drive (actually for a true Fusion drive the se is more involved but for this discussion that is enough).

As I wrote befrore I am surprised to see a non fusion equipped iMacs internal drive setup as a LVG. I don't see the sense of having a single disk setup this way.

So this may be the way new iMacs come, though the missing 1.5tb of disk make this seem wrong, or it might be a mistake when the system was configured (someone experimenting with it and forgot to put it back) or else something you did when you got the system and tried to make the UNIX partition caused this. In any case you need to contact Apple and find out what the disk configuration should look like.

The GUI Disk Utility has limited ability to deal with LVGs (though I thought the version in the build of ML that came with these systems id a better job, which is why I asked if the system has the OS and applications that came with it.

The command line diskutil does have all the tools needed to examine, create and revert LVs.

Again until you find out just what the configuration of the disk should be it is hard to say what you need to do to get this fixed. It might be as simple as going into didkutil and reverting the LVG.

So again if disks are configured as part of a LVG then the underlying physical disk cannot be manipulated in the normal ways.

good luck and post back once you find out what the configuration is suppose to be.

regards

It still looks like a Fusion setup, are you sure that this Mac does not have that?

Was my thoughts also but the OP says no and the SSD doesn't show up in the diskutil dump or the screen shot.

I still say this is a mistake, a single disk system shouldn;t be made into a LVG, plus there is also the missing 1.5tb.

Agreed, this looks wrong, I would start over but the OP seems to be saying that he can't .... and I do not know whether any form of backup exists, so am reluctant to go further with erasing the existing drive.

From what I've been able to gather from the web as I don;t have acess to one of these, is that the command line duskutil has the commands to make and break LVGs but it is unclear what happens to the data on the disk 😟

I was also under the impression that Disk Utility (the GUI version) included with the build of ML that comes on these systems should have the ability to deal with LVGs. Which is why I also asked if this was the OS that came with the machine or if he had done a clone of his older system.

Unless we can find someone who has one of these and can describe the disk setup I think the best thing the OP can do is contact Apple to get a definitive answer.

Message was edited by: Frank Caggiano - fixed typos

Agreed.

The Mac Store" who took it in, said it was a dud and got me this replacement, so I'll see if they can help me out.

Ahh Ok this is not a machine from Apple! So is it suppose to be new or is it refurb or what?

That definitely helps to make more sense of it. Have them sort it out but it sure sounds like someone was experimenting on it before you got it 😉

And please post back once it is resolved, I am really interested to know how the drive in a no fusion 2012 is setup.

good luck

BTW

But I have secure backups and will not hesitate to erase the drive and reinstall, if that is even possible.

That won't be a problem you'll just need to delete the LVG and turn the drive back into a normal single dive setup. diskutil will handle that. As I wrote I thought Disk Utility in the build of ML that comes with these systems should also be able to deal with LVGs.

Not saying the outfit you're dealing with is dishonest but you should really give the system a good going over including the version of ML that is installed on it. The build for 2012's is different then the build for older systems.

regards

Message was edited by: Frank Caggiano

See my added conment in my previous post.

use the comannd line diskutil to remove the LVG then you should be back to a normal drive