Boot Option

Abstract
This article shows how to boot terastation from a different location than /dev/md0.

Prerequisites

 * 1) You need a modified firmware: Fail Safe Firmware
 * 2) You need an additional boot device: Emergency Boot
 * 3) You need a partition to boot from, e.g. extra disk (internal or external) or from /dev/hd'x'4, example with /dev/md3:
 * 4) boot from sda1
 * 5) copy system and set start configuration

mdadm -C -n 4 -l raid1 /dev/md3 /dev/hda4 /dev/hdc4 /dev/hde4 /dev/hdg4 mkfs.xfs -f /dev/md3 mkdir /mnt/md3 mount /dev/md3 /mnt/md3 cp -a /mnt/teraroot/* /mnt/md3 vi /mnt/md3/etc/fstab /dev/md3       /               auto    defaults,noatime                0 0 /dev/md0       /mnt/teraroot   auto    defaults,ro                     0 0 proc           /proc           proc    defaults                        0 0 /dev/hda2     swap            swap    defaults                        0 0 /dev/hdc2     swap            swap    defaults                        0 0 /dev/hde2     swap            swap    defaults                        0 0 /dev/hdg2     swap            swap    defaults                        0 0 mkdir /mnt/md3/teraroot
 * 1) /etc/fstab: static file system information.

Setting boot partition option
If you have a bootable partion simply set the device you want to boot from in /etc/BOOTPART of the md0 partition, i.e. /mnt/teraroot/etc/BOOTPART after booting from sda1:

mount -o remount,rw /dev/md0 echo md3 > /mnt/teraroot/etc/BOOTPART reboot

After boot:
root@TERASTATION:~# mount /dev/md3 on / type auto (rw,noatime) proc on /proc type proc (rw) /dev/shm on /mnt/ram type tmpfs (rw,mode=1777,size=15m) devpts on /dev/pts type devpts (rw,gid=5,mode=620) /dev/md0 on /mnt/teraroot type xfs (ro) /dev/md1 on /mnt/array1 type xfs (rw,noatime) /dev/md2 on /mnt/array2 type xfs (rw,noatime) /proc/bus/usb on /proc/bus/usb type usbdevfs (rw)

Diagnosis
If you set up your system booting from a different location e.g. md4 and this partition is not mountable,


 * the system boots with md0
 * the yellow power led blinks

If the booting of md0 fails


 * the system boots EM
 * the yellow power led is on

... and of course all other leds behaviour as you know it.

Courtesy of André