iMac crashing after High Sierra clean install

[abphoto]

I am looking for some advice on why my iMac has become so unstable as to be repeatedly crashing following a clean install of High Sierra.

First, some background on the setup.

I've been running this iMac off of an external thunderbolt SSD for a few years now and that's been working just fine prior to the OS upgrade. The reason for use of the external SSD is to take the place of a broken fusion drive inside the iMac. The HDD portion of the fusion drive is completely broken...as in making clicking sounds when the unit first powers up. For some reason the unit also takes a lot longer that it used to before getting startup chime/bong and then longer still before I get to the OS. I'm wondering if the broken hardware is causing the issue or it it's something else. Is there any way to completely disable the internal drive so the Mac does not even try to access it first?

Thanks in advance for any suggestions.

 

[briloronmacrumo]

I am looking for some advice on why my iMac has become so unstable as to be repeatedly crashing following a clean install of High Sierra.
First, some background on the setup.

First thing: post details on which iMac( year and model would be a good start ) you're describing. That would enable folks to provide more specific feedback on the fusion drive. Also, I'm sure it would be helpful to have some diagnostic output from some system utilities ( at a minimum a disktuil list in Terminal.app and probably sysdiagnose output ---a shortcut to running sysdiagnose is to hold down the shift, control, option and command keys and press the '.' key. About 30 seconds to a minute later a Finder window will open with the zipped report). Lastly, IIRC, there are situations where High Sierra's APFS doesn't play well with Fusion drives and I'm betting there are many MacRumor's threads ( and many on Macintouch ) detailing the issues. Maybe look for those threads.

 

[abphoto]

Thank you for the response. iMac (27-inch, Late 2013).
I'm in safe boot mode now and it's not crashing, so there's obviously something odd when running in full user mode.
I will run a diagnostic report and post that shortly.
Regarding the AFPS issue..wonder how that effects things based on the fact I'm not booting form the fusion drive. Maybe ther mere fact that I fusion drive, even though broken, exists on the device is causing a problem. But, gain, not crashing in safe boot mode, so who knows!

 

[abphoto]

Update: I think I've determined the problem and have gotten things working again. No more crashes.
There was apparently a problem with the formatting of the internal HDD side of the (former) fusion drive. I've reformatted it and things have been working MUCH better since. The one things that still confuses me is that disk utility only sees it as having 50.49 GB of total capacity. It not a problem as I do not plan to use it anyway. Thanks again to briloronmacrumo for the response that got me thinking.

 

[Fishrrman]

If the HDD is completely dead, I'd try a complete erase of the internal SSD (portion of the fusion drive).

Then, I'd install a copy of the OS onto it and see if I could boot that way.

Even on a 2013 model, I sense that the SSD drive that Apple was using back then (should be 128gb) would be faster than an external thunderbolt drive.

Final thought:
I'd prefer Low Sierra over High Sierra for now. Maybe forever..!