On Mon, Apr 13, 2015 at 10:02:15PM -0400, Nico Kadel-Garcia wrote:
> 
> Been there, done that. Don't have to make this stuff up, I spent some
> time *designing* Linux based storage servers, but it was more than 5
> years ago.
> 

Yes, much has changed in 5 years. Some improvements. Bootable RAID1 on of them.

> Are you finding that it actually works? Would you please post an
> /etc/fstab from a working system to help verify that it works?

# /etc/fstab
UUID=9929c664-7934-40ac-9ecf-28cfa64844d8 /                       ext4    defaults        1 1

[root@daqshare ~]# blkid
/dev/md0: UUID="9929c664-7934-40ac-9ecf-28cfa64844d8" TYPE="ext4" 

# mdadm.conf written out by anaconda
ARRAY /dev/md0 level=raid1 num-devices=2 UUID=93f3fadc:138a6ace:3b0b01ea:c2b3f631

[root@daqshare ~]# cat /proc/mdstat
Personalities : [raid1] 
md0 : active raid1 sdb1[1] sda1[0]
      40959928 blocks super 1.0 [2/2] [UU]
      bitmap: 0/1 pages [0KB], 65536KB chunk

[root@daqshare ~]# more /boot/grub/grub.conf
# grub.conf generated by anaconda
default=0
timeout=5
title Scientific Linux (2.6.32-504.12.2.el6.x86_64)
      root (hd0,0)
      kernel /boot/vmlinuz-2.6.32-504.12.2.el6.x86_64 ro root=UUID=9929c664-7934-40ac-9ecf-28cfa64844d8 rd_MD_UUID=b95b94be:ad2afad9:8200c707:6806aece
 rd_NO_LUKS  KEYBOARDTYPE=pc KEYTABLE=us LANG=en_US.UTF-8 rd_MD_UUID=93f3fadc:138a6ace:3b0b01ea:c2b3f631 SYSFONT=latarcyrheb-sun16 crashkernel=auto rd_N
O_LVM rd_NO_DM
      initrd /boot/initramfs-2.6.32-504.12.2.el6.x86_64.img

Grub is installed on both disks:
# grub
device (hd0) /dev/sda ### (/dev/sdb for the second disk)
root (hd0,0)
setup (hd0)

the machine boots from either disk (other disk should be disconnected)
or if the order of disks is changed.

One caveat with SL6 is that the md0 array *MUST* be defined in /etc/mdadm.conf *AND*
you have to rebuild initramfs to have it included inside the copy of mdadm.conf
inside initramfs. (or dracut will fail to assembled the raid arrays).

-- 
Konstantin Olchanski
Data Acquisition Systems: The Bytes Must Flow!
Email: olchansk-at-triumf-dot-ca
Snail mail: 4004 Wesbrook Mall, TRIUMF, Vancouver, B.C., V6T 2A3, Canada