Haines Brown <haines@???> wrote:

> In the partitioning scheme, sda is HD ST1000DX002-2DV1. It has a primary
> partition that is bootable and the mount point /.

You probably want to set this partition to unused (or whatever it's called, it's a looong time since I last did this) so that it doesn't appear in the mount point table (eventually in fstab of the new install). I think what you are telling it is that you want sda1 to mounted as / IN THIS INSTALLATION and that then clashes with your new / (on sdc) that you're trying to install to.