Missing CoreStorage partition

[neuropsychguy]

I'm running a late 2012 iMac running El Capitan with a 1TB Fusion drive. today my iMac froze and was unresponsive so I did a hard restart. After the restart it was not responsive so I did a hard power off. It turns out that it was probably running the latest system update at the time so turning it off the second time was bad. I turned it back on and let it start up for a few minutes. It got to the Apple loading screen, then turned black with the "No symbol" appearing on the screen (verbose start showed it was stuck looking for the root drive). After starting in recovery mode disk utility showed only the 1TB HDD and not the CoreStorage SSD part. diskutil cs list gives the error: "no corestorage logical volume groups found". Nothing I've tried so far (e.g., cat /dev/random > /dev/disk0) has worked. Any suggestions for how to see and 'reattach' the other 128GB Fusion drive so I can get my computer back up and running. Right now it just thinks I have a 1 TB hdd instead of 1.2 TB (which is a problem for trying to restore my Time Machine backup because I was down to about 15 GB free space).

 

[Weaselboy]

Do a command-option-r boot to Internet recovery (this is different than a command-r recovery). Select your wifi and you will see a spinning globe then the recovery utility. Start Disk Util from there and tell me what you see. Also run "diskutil list" (without the quotes) in Terminal from recovery and tell me what you see.

I don'r think an aborted update would cause this. It sounds like you may have a hardware issue going on with perhaps the 128GB flash module failing.

 

[neuropsychguy]

Not in recovery but this is my current output from diskutil list. There should be a 128GB CoreStorage volume in there. It is looking like a hardware issue because nothing I've tried has fixed the issue yet. Off to repairs this computer goes.

/dev/disk0 (internal, physical):

#: TYPE NAME SIZE IDENTIFIER

0: GUID_partition_scheme *1.0 TB disk0

1: EFI EFI 209.7 MB disk0s1

2: Apple_HFS Untitled 999.3 GB disk0s2

3: Apple_Boot Recovery HD 650.0 MB disk0s3

 

[Weaselboy]

Yeah... looks like a hardware issue. You should see disk1 as the 128GB flash drive and disk2 as the core storage 1.2TB Fusion logical volume. It appears the 128GB bit the dust and of course that broke the Fusion logical volume.

 

[neuropsychguy]

Yeah... looks like a hardware issue. You should see disk1 as the 128GB flash drive and disk2 as the core storage 1.2TB Fusion logical volume. It appears the 128GB bit the dust and of course that broke the Fusion logical volume.

There was some command I ran in Terminal - I can't for the life of me remember what it is now - that is analogous to

diskutil list

but it showed the missing 128GB. I'm still going to send this off to be repaired because it's a work computer and I don't have time for it to be out of commission and I don't have time to tinker with it but one of these days I'd like to find that command again just to add to my knowledge base.