Booting to alternate disk using GRUB
Posted on 2006-05-30
Suppose you have a box running Linux and using GRUB to boot. I doubt it matters, but let's say its RHEL3.0. This is a BC/DR scenario, the processes and situation are not optimal. This is about quickly recovering functionality, and not about doing things the "best" way.
This box has two physical disks - hda and hdb. Let's say they're identical size/geometry. hda has the current running OS, nothing is on hdb. Perhaps hdb has been partitioned and blank filesystems put on it, but no data. They're not necessarily even mounted (or in fstab).
Let's say I need to recover another system for BC/DR purposes. I load my tape backup software on this server (installing somewhere on hda) and can now access my backup tapes. I restore the other system to hdb - dump all the filesystems down to that previously blank drive. The system being restored is also RHEL3.0. I'm restoring / and everything else from tape.
But I didn't go thru an install. hdb has no MBR. There's an MBR and GRUB on hda. The restored system is on hdb. So how do I boot to hdb?
Remember, this is a BC/DR scenario. A manual boot process is OK, the goal is to get the restored-from-tape OS and software, dumped on hdb, booted and running.
1) About the MBR...
a) Does the fact that hdb doesn't have an MBR make any difference?
b) If so, is there an easy way to get one on there?
c) If so, HOW?
2) About booting...
a) Can I boot the OS on hdb from the GRUB on hda?
b) If so, HOW?