I have a 5,1 iMac with a broken internal disk. After many attempts I got a working installation of Ubuntu 20.04.03 on an external USB drive.
The boot is very long due to a repeated message:
COMRESET failed (errno = -32).
dmesg | grep ata
reports:
ata5: SATA max UDMA/133 abar m1024@0x88305000 port 0x88305200 irq 27
...
ata5: COMRESET failed (errno = -32)
ata5: reset failed (errno=-32), retrying in 33 secs
...
I need to skip any check over broken disk.