OS Upgrade Failed; Disk Utility Shows an SSD and won't boot
I'm updating my Mac mini (Late 2014, 1TB HDD) from OS X El Capitan to Big Sur. 60 GB of free space on the target partition, but the install failed and Disk Utility now shows I have both an HDD and an SSD drive.
My 1TB SATA HDD is partitioned in half: MacOS and MacOS-Clone (I cloned my El Capitan install and data so I can run legacy software).
The Big Sur install on the MacOS partition failed at the dreaded "one minute remaining" mark. The drive rebooted several times before I saw the prohibitory symbol (circle w/ line through it).
I rebooted in Recovery mode and ran Disk Utility; no errors. But the MacOS-Clone partition started up — not my previously designated startup disk.
Disk Utility reports that I now have two drives in the machine: Apple HDD (disk1) and Apple SSD (disk0). Apple HDD has two partitions: MacOS-Clone and Untitled (formerly my MacOS/startup disk and hopefully my Big Sur partition).
The "new" disk is named Apple SSD SM0128G Media, an Untitled 121.33 GB PCI Internal Physical Disk.
I have a Time Machine backup from the old MacOS but no drive to restore it to, unless I overwrite my MacOS-Clone.
I'm thinking I will need to erase the entire machine and start with a fresh install of El Capitan (the last OS that worked properly).
Any thoughts are welcome. If you want more tech details, some appear below.
Mac mini (Late 2014)
Hardware Overview:
Model Name: Mac mini
Model Identifier: Macmini7,1
Processor Name: Intel Core i5
Processor Speed: 2.6 GHz
Number of Processors: 1
Total Number of Cores: 2
L2 Cache (per Core): 256 KB
L3 Cache: 3 MB
Memory: 16 GB
Boot ROM Version: 431.6.0
SMC Version (system): 2.24f32
Apple SSD SM0128G Media
121.33 GB PCI Internal Physical Disk
One GUID Partition: Untitled (121GB)
S.M.A.R.T. status: Verified
Child count: 2
Type: Solid state
Device: disk0
APPLE HDD HTS541010A9E662 Media
1 TB SATA Internal Physical Disk
Two GUID Partitions: Untitled (443GB) and MacOS-Clone (556GB)
S.M.A.R.T. status: Verified
Child count: 4
Type: Disk
Device: disk1
Mac mini, OS X 10.11