Disabling SCSI parity checking to dump disk on ACB4000 MFM-SCSI adapter?

[Michael Engel]

Hi,

still working on backing up the Tektronix 440x disks. My current problem 
is that the ACB4000 SCSI-to-MFM adapter doesn´t support SCSI parity.

I finally managed to find a PCI SCSI controller (Adaptec 2940) and a 
Pentium 4 PC with PCI slots and installed OpenBSD 6.7. I disabled parity 
checking in the Adaptec BIOS config and it detects a disk at ID 0 with 
no name. So far, so good.

However, OpenBSD always seems to enable SCSI parity and complains about 
disk parity errors. I tried to disable all lines in the aic7xxx and 
ahc_pci driver source files that seem to enable parity, but nothing 
seems to make a difference. The drive/ACB4000 is not detected by 
OpenBSD, I get a "device not configured" error when accessing the disk 
device files (/dev/sdxc and /dev/rsdxc).

Do you know if is there another OS which would make it easier to change 
crucial SCSI parameters in the driver (config) or maybe a specialized 
tool that could help me to image the disk?

-- Michael