Creating an MD Root Mirror in Linux

For whatever reason, you originally set up your Linux host without a root
disk mirror and now you want it mirrored.  One could say "just re-install,"
but surely there is another way, and there is.  The solution isn't quick
or simple, though it isn't impossible.  Our host details are:

Missing GRUB Config in Linux

Having recently written up how to restore GRUB to a missing / corrupted
master boot record (MBR), it seemed appropriate to follow up with
resolving a missing GRUB config file.  Our host details for this
situation are:

Disk Cloning in Linux

A while back, I wrote up how to clone a disk in Solaris and in FreeBSD,
yet somehow managed to overlook writing up how to do so in Linux.
This write up is to rectify just that, how to clone a disk, in this case,
the root disk, in Linux.  The following are our setup details:

GRUB, a Corrupted MBR, and Linux

Recently, after cloning a root disk in Linux, I ran into an issue because
I failed to setup the master boot record (MBR) on the alternate disk.
Everything else was configured, including the boot image files and grub
configuration under /boot/grub, but the MBR wasn't setup.  The following