iMac 5K Fusion Drive won't mount / boot

[SadMinky]

I was working in Adobe Photoshop with some large files, and I believe it filled the Macintosh HD with scratch files. The system locked up and I rebooted it. It did not startup, and would just hang. I'm running El Cap, on a 2TB Fusion Drive, iMac 5k.

I brought the system up as a target drive, running Disk Tools and Drive Genius 4 from my Macbook Pro running Yosemite. It reports nothing wrong with the hard drive, but it will not mount the Macintosh HD.

Verifying and repairing partition map for “APPLE SSD SM0128G Media” sometimes reports "Error: A disk with a mount point is required."

I sometimes also get: Disk Utility stopped repairing “Macintosh HD” Unrecognized file system

Running verify reports: The volume Macintosh HD appears to be OK.

I have been able to clone the drive (and boot from it) and could just restore it back to this one (I think), but I want to try and "fix" it to resolve the issue.

Info says there are 0 bytes available on the drive, which was my suspicion. How can I read AND edit the contents of the drive? I want to delete a couple files, and I'm pretty sure it will mount / boot again.

In single user boot I see things like: (I know very little unix, and DOS was a long time ago)
Error replaying the journal
Failed to open / crete the journal

fsck -fy reports no errors
mount -uw / reports error on mount -1, permission denied

Any thoughts

 

[SadMinky]

I think I have found my own fix. I wasn't able to "fix" the drive format and mount it, so in frustration I tried to erase and / or restore it but ran into permission issues.

I couldn't restore to the fusion drive, so I split it from terminal, forcing it to reformat both drives, then joined them back together as Macintosh HD.

That seems to have worked, I am now using Carbon Copy to restore my drive clone. Fingers crossed. . .

 

[maflynn]

I ran into some odd issues with Fusion, but it was boot camp related. That is I tried to create a windows partition, it failed to install, but then I couldn't remove the partition. It was so bad, I couldn't even unfuse the drives, but had to totally delete the partitions via gpt.

I know this issue is totally different, but it makes you wonder if there are some latent bugs hiding that you or I unwittingly came across.

 

[SadMinky]

I think because it is a "virtual" volume, anytime something goes wrong on the individual drive level, the software / drivers / etc don't realize it because it views it as a "whole" device and not a collection of parts. My problem, I think, came down to corrupted permissions on one drive, not letting me format or do other operations to restore the OS or a backup. I'm not out of the woods yet, I'm half way through a 24 hour or longer restore, since I'm running off a really, really slow portable drive that I turned into a cloned boot drive.

 

[maflynn]

I think because it is a "virtual" volume, anytime something goes wrong on the individual drive level, the software / drivers / etc don't realize it because it views it as a "whole" device and not a collection of parts.

for a lack of a better understanding, Fusion reminds me of a RAID 0 setup. When one drive in the array goes south, you lose the entire logical volume. The same with Fusion.

Side note, We usually here how going with a RAID setup is not recommend because of that issue, but here we have the Fusion drive - kind of weird.

Side note #2. I split up my Fusion drive, in part because of the issues incurred, but also because at the time, Windows was my main OS and I wanted that on the internal SSD. The issues I had with Fusion and installing windows drove me to splitting up the drive.

OS X is now running on a larger external USB 3 SSD and performance is great with that, and Windows is rocking on the 128GB SSD internally

 

[hfg]

for a lack of a better understanding, Fusion reminds me of a RAID 0 setup. When one drive in the array goes south, you lose the entire logical volume. The same with Fusion.

Of course, if a alternative is to simply put all of your stuff on either a single hard disk ... or a single SSD, and one drive (now your only drive!) goes south, you also lose everything.

BACKUP, BACKUP, BACKUP

(This is generic advice, not directed at any specific poster here )