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[Update] I decided to try installing Mac OS Sierra on another hard drive to see if Mac OS High Sierra is in play with this issue. In doing so, it rendered my Mac OS High Sierra drive unbootable somehow, although my data seems to be in tact on the file system. Since I used my back up disk for my orig...

Hi BlueMac77, Out of curiosity, what is the SMC version on your Mac? It should be on the Hardware Overview pane of the System Report app. I have zapped my PRAM but not with the drive removed. I will try that and report back. I can also try running the disc repair from the recovery drive, but this se...

Hello, I wanted to update this thread as the situation has changed for one of the drives. As @Woodstock mentioned how low level this issue may be, I unplugged both the internal, SATA ASUS drive (BW-16D1HT) and the USB Pioneer drive. I also unplugged the computer. Upon rebooting, the Pioneer now work...

I am not sure if anyone else has seen this, but it is utterly confounding. I updated to High Sierra recently (to keep getting security updates) on my 2010 5,1 Mac Pro and with the update came a firmware update. I am now at macOS High Sierra 10.13.6 (17G11023) (High Sierra) and firmware was upgraded ...