Well I'm in a bit of a pickle. I was wiping and re-installing my 2009 iMac to give to my in-laws, and the process of trying to erase my homemade fusion drive seems to have left the disk in a strange and unusable state. Before this, I was happily running Yosemite (and Mavericks before that) with the fusion drive, working fine. It's a 500 GB spinning drive with a 256 GB Flash drive in place of the superdrive (using drive doubler). Initially I tried to do a "secure erase" with 3 overwrites, but that didn't seem to be making any progress, so I switched to single overwrite and that failed to finish with an error message that unfortunately I didn't write down. Here is the summary of the current state of the drive. I'm booted off a flash stick imaged with a Yosemite installer. Get info for the drive: Name: fusion Type: Logical Volume Group Disk Status: Online Total Capacity: 754.96 GB Free Space: 41 KB Physical Backing: disk0s2, disk1s2 So far so good, I think. First attached crappy screenshot shows the log of when I tried to "repair disk". Second attached crappy screenshot shows what disk utility tells me when I try to partition the drive. I can't make sense of all the conflicting messages. It knows it's a fusion drive, knows it's 750 GB, but will only let me have a 500 GB partition, and won't let me reformat. At one point in the repair disk log (not shown in screenshot) it said "can't repair volume while it's in use", but I'm booted off a different drive, so how is it in use. Can anyone give me some pointers how to get this working again, and maybe some insight as to why it got screwed up this way in the first place?