Hello,
I am trying to convert a single-drive Centos 7.2 installation with LVM into a two-disk mdadm mirror with mrrored LVM. I was able to follow the excellent instructions at:
http://www.dgoradia.com/creating-a-raid1-mirrored-on-an-existing-centos-on-lvm/
and did create a two-disk mirror of both the original boot partition and the LVM partition. When I boot off a live Centos 7.2 DVD with the mirrored drives installed it does find the mirrors, and I can fsck and mount the boot and LVM filesystems in it.
[root@new-host-4 ~]# lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
sda 8:0 0 465.8G 0 disk
sda1 8:1 0 1G 0 part
md126 9:126 0 1024M 0 raid1
sda2 8:2 0 115G 0 part
md127 9:127 0 115G 0 raid1
centos-root 253:3 0 40G 0 lvm
centos-swap 253:4 0 9G 0 lvm
centos-home 253:5 0 25G 0 lvm
centos-var 253:6 0 40G 0 lvm
sdb 8:16 0 465.8G 0 disk
sdb1 8:17 0 1G 0 part
md126 9:126 0 1024M 0 raid1
sdb2 8:18 0 115G 0 part
md127 9:127 0 115G 0 raid1
centos-root 253:3 0 40G 0 lvm
centos-swap 253:4 0 9G 0 lvm
centos-home 253:5 0 25G 0 lvm
centos-var 253:6 0 40G 0 lvm
sr0 11:0 1 4.4G 0 rom /run/initramfs/live
loop0 7:0 0 20K 1 loop
loop1 7:1 0 4.3M 1 loop
live-osimg-min 253:2 0 8G 1 dm
loop2 7:2 0 1G 1 loop
loop3 7:3 0 8G 1 loop
live-rw 253:0 0 8G 0 dm /
live-base 253:1 0 8G 1 dm
live-osimg-min 253:2 0 8G 1 dm
loop4 7:4 0 512M 0 loop
live-rw 253:0 0 8G 0 dm /
[root@new-host-4 ~]#
However these instructions are specific to Centos 6, and the section for installing a bootloader on the new mirror completely does not apply in Centos 7. In Centos 7.2 there does not seem to be any commandline utility that provides a "grub>" command prompt, ant the grub binary itself is replaced by a bunch of "grub2-*" executables.
Can anyone explain how to reinstall the bootloader on the new mirror? The Centos 6 instructions say it must be installed separately on sda1 and sdb1.