It took me four hours to diagnose and cure problems caused by Apple Tech Support for a consulting client of mine, who had called Apple after a power failure.
In a nutshell:
- After a power failure, the iMac 5K would no longer boot.
- Apple support failed to diagnose the problem: I found file system damage to the boot volume (APFS) on the internal iMac 5K SSD. It was non-repairable by Disk Utility. So much for APFS being resilient in the face of power failures.
- Apple support left the client with a damaged file system on the internal SSD boot drive; the internal SSD remained unbootable and unused and useless.
- Support directed the client to reinstall macOS, but reinstall of macOS occurred onto an old and slow USB3 hard drive. The install converted the hard drive to APFS (horrible performance on hard drives). When I got there the speed was horrible, with the hard drive making constant noise as APFS banged the drive heads around mercilessly with constant head-seeking.
- The client lost some stuff because of this fiasco because Time Machine had not run for some days. Nothing major, but some stuff.
- Adobe Lightroom was left unusable (could not find any files) since the macOS install shoveled everything into a subfolder on the hard drive which had been put into duty as the boot drive.
What a mess. The performance was so bad that hardly anything could be done without great patience. Ultimately I erased the internal SSD to create a clean file system, and got things back onto it and booting off it. I also set up the client with a better strategy should this happen again, with an external SSD for a boot clone, for fast bootable recovery.
A solid backup strategy is important—this client could have done a better job at it, but there need not have been such a godawful mess; Apple support screwed up at every step from what I can tell.