Bug#380049: debian-installer/etch bug report
> The machine is set to install on /dev/md0 raid1. The installer worked
> like a charm, and on reboot into the live system I end up with major
> failure, the scripts try to start the raid system with mdrun but I end
> up with the error;
> "mdadm: cannon open device /dev/hda5: Device or resource busy"
> When I attempt to mount /dev/hda1 I end up with the same error.
that is a known problem of the mdrun initramfs boot script.
it got dropped for proper hook scripts,
you need newer initramfs-tools > 0.70 and mdadm from unstable.
try to fetch those before reboot.