I'm installing ascii on a disk, sdc, in a machine that has two other disks,
one of which, sda already has a bootable devuan jessie on it.

The installation goes well until I go to write my partitioning of sdc to
disk. I get the error message: "Two file systems are assigned to the same
mount point (/): SCSII (0,0,0), partition #1 (sda) and SCSI3 (0,0,0),
partition #1, (sdc).

It is true that partition 1 of sda is a bootable primary partition, and
I want to do the same for sdc. I've always had multiple independently
bootable disks with their own GRUB on a machine. This is the first time
I've run into trouble with it. In installation options for sdc, I did
ask to have a MBR installed.

Why does an installation on one disk care about what happens to be on
another unmounted disk?

Haines Brown