Ubuntu – Advanced configuration of Grub2 for RAID5 + Encrypted LVM where /boot needs redundancy

There are two ways to encrypt an LVM volume:

1. You create an encrypted partition, create the PV inside it and then the whole PV is encrypted
2. You create a normal LVM, create LV inside it and then create an encrypted partition inside the LV.

If you use method 1 your root partition is encrypted. You might have gotten an emergency shell.

If you use method 2 you might want to leave the root unencrypted to simplify recovery if something goes wrong. Normally the root partition should hold system file, not private files.

You need to install GRUB to the MBR of both drives, and you need to do it in a way that GRUB considers each disk to be the first disk in the system.

GRUB uses its own enumeration for disks, which is abstracted from what the Linux kernel presents. You can change which device it thinks is the first disk (hd0), by using a "device" line in the grub shell, like so:

device (hd0) /dev/sdb

This tells grub that, for all subsequent commands, treat /dev/sdb as the disk hd0. From here you can complete the installation manually:

device (hd0) /dev/sdb
root (hd0,0)
setup (hd0)

This sets up GRUB on the first partition of the disk it considers to be hd0, which you've just set as /dev/sdb.

I do the same for both /dev/sda and /dev/sdb, just to be sure.

Edited to add: I always found the Gentoo Wiki handy, until I did this often enough to commit it to memory.