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I had a mid-2011, 2.5GHz, AMD graphics, Mac Mini with an SSD and HDD using OWC’s dual drive setup. The SSD drive had the OS (10.11 I think) and the HDD had my home folder and an old version of OS X (10.7 I think). I was running this setup for several years, with updates to the newer OS, with no permission issues. The computer had a logic board or GPU failure (wouldn’t boot, power light on, no chime, blank screen, the fan immediately revs to full speed) so I purchased a replacement Mac Mini with the same specs and moved the two drives to the new machine. The new machine will not boot as intended.

When I try to boot normally, the computer gets to the Apple logo and the spinning icon for a half second before shutting off. When I boot from a USB installation disk, I can get to Disk Utility, etc. The Startup Disk options screen does not show an OS on the SSD, only the HDD. Everything shows “OK” when running First Aid on SSD. Running First Aid on the HDD shows a permissions problem that may prohibit booting. Using Verify in the menu I can navigate the contents of the HDD but nothing for the SSD.

A couple of places on the web have recommended creating a backup home folder on the SSD boot drive when creating the dual SSD/HDD setup, in case of permission errors or directory corruption, but they don’t explain what the consequences are or how to fix it if you haven’t done this and run into problems. I can’t remember if I created the backup home folder on the SSD.

So, what is keeping my Mac Mini from booting? Is there a corrupt directory or disk permissions gone haywire? If the problems involve my home folder, is there a way to create a new home folder on the SSD to make the drive bootable and then point the OS to the correct home folder on the HDD, all without overwriting anything currently on the SSD? I have a feeling I’ll be mucking about in the Terminal.

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    Both devices were in a computer which failed catastrophically somehow. The possibility of both logical damage (directory structures & whatnot) and physical damage (destructive power frying the disk controllers) are possible. It also could just be a bad ribbon connector cable. Sometimes you can't tell just from a physical inspection if it has become damaged. See if you can find a new cable. In the long run, the best bet is to somehow move all the data from the HDD and start fresh. I've had to do it several times over the years.
    – IconDaemon
    Aug 27, 2022 at 0:59
  • The ribbon connector situation in this type of setup is a bit precarious. I’d have to order a new one. Before doing so I checked the SSD in an external enclosure with a working computer, without the ribbon cable. It did not mount. I think you are right about it possibly being physical damage to the drive itself.
    – Kev
    Aug 27, 2022 at 19:34

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  • If the new Mac Mini was manufactured after the macOS version you are trying to boot, it may not be supported and you may need to update the system first (installing a newer macOS to the existing disk via a bootable installer should preserve data, but you should make a backup just in case).
  • Try holding option/alt when booting and selecting the disk (to rule out Startup Disk issues - the Mac may be looking for another drive).
  • Try booting in verbose mode (Cmd+V) to see if there are any errors. Tip: if the text scrolls too fast, you can use a camera to record it and pause it or use slo-mo mode.
  • Try swapping the positions of the HDD and SSD (if the system at tries to mount the home by path e.g. /dev/disk1, it may make a difference). Depending on how the "external home folder" was set up, you may also need to update the path to match the HDD's location in the new machine. Also, if any other storage device/flash disk/card reader/... is connected, try disconnecting it first.
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  • Do you mean update the OS on the HDD or the SSD? I don’t necessarily need OS X 10.7 on the HDD, but maybe update it so I can at least get my computer booted? I probably should have deleted 10.7 sooner than later because by the time I was using 10.11 I was no longer using 10.7. I’m unclear if I could even still boot from 10.7 on my old machine before it died. If I tried to update the OS on the SSD I have a good feeling that data will be overwritten, since the SSD doesn’t seem to be read correctly.
    – Kev
    Aug 27, 2022 at 6:39
  • * A couple of lines stood out to me booting in verbose mode (I had totally forgotten about this mode. Thank you.) PCI configuration changed… Pthread support ABORTS when sync kernel primitives misused Then the end of the screen: Devfs_kernel_mount: failed to find directory ‘ /dev’ , 2Kernel is LP64 Kext loading now disabled. Kext unloading now disabled. Kext autounloading now disabled. Kernel requests now disabled. Syncing disks… Killing all processes Continuing Done CPU halted
    – Kev
    Aug 27, 2022 at 6:41
  • Matching the Volume UUID to the BSD Name indicates to me that the computer was trying to boot from the OS on the HDD. As mentioned above, I’m not sure I could even still boot from 10.7 on the HDD in my old machine, before it died. So, I would think it failing to find directory /dev wouldn’t be the problem we’re looking for. Is there something else for me to search for in the verbose startup?Other recent observances in Disk Utility and System Information lead me to believe my SSD isn’t mounted. I can see the image but no indication that it’s mounted.
    – Kev
    Aug 27, 2022 at 6:42
  • * Swapping HDD and SSD in the enclosure produced the same results, just with a change in bay name, BSD name, BSD root, etc. I’m not sure what you mean by “update the path to match the HDD’s location in the new machine.” Where would that be changed?
    – Kev
    Aug 27, 2022 at 6:44
  • Do you have access to a working Mac? In this case I would drop the SSD into an external enclosure and check the drive contents using Disk Utility and Finder or Terminal to rule out whether the drive is simply damaged or dead. If you can’t mount it, read from it, or check it for errors from a working Mac, the drive itself likely has physical damage and needs to be replaced.
    – dr.nixon
    Aug 27, 2022 at 17:55

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