Bug#662086: Possible resolution: Re: grub-install failed with raid+lvm

[John Hanson <crayz9000@gmail.com>]

I ran into this same issue with a Debian Wheezy amd64 netinst disk
(Binary-1 20120201-15:35).

A quick Google search for some of the error messages turned up this post:
http://lists.alioth.debian.org/pipermail/pkg-grub-devel/2011-June/012317.html

Like him, after mounting /proc manually while chrooted into /target,
the grub-install succeeded from the Debian installer.

Looks like grub-probe is basically failing for RAID and LVM because
/proc is not mounted before grub-installer is called.

Hope this helps.