Hard Drive Erase Help

Easiest solution is to use the Partition Scheme's dropdown menu to reselect one partition. Set the format to Mac OS Extended, Journaled, Then click on the Apply button. This will return you to a single partition on the drive to use with OS X.

I think I know the issue. This is your startup drive. You cannot make changes to it while booted from it. You must use the Recovery HD partition to make the change.

Drive Partition and Format

1. Boot to the Recovery HD:

Restart the computer and after the chime press and hold down the COMMAND and R keys until the menu screen appears. Alternatively, restart the computer and after the chime press and hold down the OPTION key until the boot manager screen appears. Select the Recovery HD and click on the downward pointing arrow button.

2. When the main menu appears select Disk Utility and click on the Continue button. After DU loads select your hard drive (this is the entry with the mfgr.'s ID and size) from the left side list. Click on the Partition tab in the DU main window.

3. Select the partition you don't want at the bottom of the partition map, then click on the Delete [-] button. Click on the Apply button.

4. Now use the triangle gadget in the bottom right corner of the remaining partition and drag it to the bottom to make a single partition. Click on the Apply button.

For some reason your internal drive is listed as a Logical Storage Volume. Not sure how it got like that and not sure what to do about it.

The Top Most name should be the Drive Manufacturers name and or model number with the size of the drive listed as well like this.

I have seen this one other time and do not know how the person fixed it.

Why where doing the erase and reinstall? If it was because of problems with the system those problems may of started when your drive got converted, somehow, to a Logical Storage Volume.

I'd suggest you just Replace the drive but that isn't that easy on a iMac.

Good Luck & Best Wishes.