Replacing disk in Linux Software RAID 1

[Nigel Wade]

Michael E. Webster wrote:
> Michael,
> 
> Probably - I went with "ghost" because I had a boot floppy handy.

You should not need to ghost. Add the new drive as a hot spare and md should 
  take care of building the new drive whilst the system is running (it does 
need to be partitioned correctly first).

> 
> The main thing is to get the MBR from that first drive - without it,
> you're out of luck.  
> 
> In software RAID, the MBR is only written to the first drive, which
> really doesn't make sense.  I would think that if you had the first
> drive fail, you should be able to boot off the second one - IMHO.
> 
> 
> Mike.
> 
> 

I don't think that's right.

In the case of lilo it writes MBRs such that each drive will boot from 
itself, and either drive can work with the other removed. OTOH, due to the 
way grub works, only one drive can be used as the boot device (each will try 
to boot from the same drive).

At least this was the case in RH9 which is the latest mirrored boot system 
I've setup. It's entirely possible that lilo has since been broken so that 
it no longer handles booting from mirrored disks.

-- 
Nigel Wade, System Administrator, Space Plasma Physics Group,
             University of Leicester, Leicester, LE1 7RH, UK
E-mail :    nmw at ion.le.ac.uk
Phone :     +44 (0)116 2523548, Fax : +44 (0)116 2523555