Install of catalina hung and now is says have a hardware error

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Ive tried to boot my iMac using the macbook with the MacBook in target disk mode.

I can't see the iMac disk in finder but I can see it in disk utilities.

If I do the reverse and start the iMac in target disk mode and use the laptop as host I still can't see the iMac files in finder.

If I run disk utilities and first aid it says there are errors. "Fusion data structures are invalid"

Im pretty sure the iMac hung because it ran out of disk space during the OS X Catalina update. It should have been OK with 23G of space.

Ive since tried to do a recovery using Stellar data recovery. Its seem to have recovered most files but the main problem is years of photos all seem to be corrupted. JPEG files won't open. "Unrecognised file format." The disk may have been encrypted and this is causing problems.

I tried to install Sierra from my laptop with the iMac as a target disk. It seemed to complete but on reboot restarted the Catalina install.

I think the way forward is to somehow get access to the iMac disk and delete some files to make space. Not sure how to make this happen. I also intend to buy another hard disk and install it in the imac. I may have more of a chance with the current disk removed and run up as an external data drive. In the interim I will contact Stellar and see if they can help with the corrupted jpg files.

Any advice?

Hi

This suggestion may fix the drive problem but it will erase all data. I'm after a way of recovering the data, particularly the photos if possible. This article suggests I will not be able to recover any data for the drive.

https://medium.com/macoclock/its-2020-hard-life-lesson-of-owning-an-imac-with-a-fusion-drive-908299a8bd1c

I thought the SSD part of the fusion drive was used like a cache. It appears that data is stored on both the SSD and the conventional disk. If one or the other becomes corrupted can data be recovered? Is it possible to recover data using software such as Stellar data recovery?

I purchased stellar data recovery. It has completed its data recovery but all of my photos are corrupted. Not a single jpg file can be recovered. They also sell a photo recovery software to repair them but I am reluctant to buy this. The video link I posted suggests that fusion drive failures result in data not being able to be recovered. My Mac was purchased in 2016 and is a late 2017 27inch 17,1. I can't seem to find out if they had a standard hard disk and an SSD acting as a fusion drive. or a single disk with build in SSD. All Mac shops in Australia are closed due to the virus and my iMac is just outside its warranty period by three months. Perfectly designed to meet its warranty period.

Might need to open it to see how its configured.

Hi

thanks for the reply but I dont have a Time Machine backup.

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Ive tried to boot my iMac using the macbook. I can't see the iMac disk in finder but I can see it in