[CentOS] Raid Cards

[Les Mikesell]

On Fri, 2006-06-09 at 23:19 +0800, Feizhou wrote: 
> > 
> >>>I just looked at the boot sector on the 3 machines that I have running 
> >>>software raid1.  It looks like the installer got it right on all 3.  
> >>>IIRC, one was installed as CentOS 4.1, another as 4.2, and another as 4.3.
> >>
> >>The installer will install grub. Just not properly. If the first disk 
> >>dies, when the box comes up, the previous second disk grub stage 1 will 
> >>load but it will not look for the stage 2 on the current disk and 
> >>therefore fail.
> > 
> > 
> > That will depend on what your bios does when the first drive fails and
> > whether you've had to move it to make it boot at all.  On the scsi
> > systems where I've used it, the 2nd drive will boot and everything
> > on the cable shifts up if the first drive fails or is removed.
> > IDE systems are different - and normally won't boot if a failed drive
> > is still connected.
> > 
> 
> Hmm, does it come back up on a scsi based system?

Mine does but it may depend on the bios.  

> I cannot remember but if the second disk's grub stage 1 does get loaded, 
> it tries to load stage 2 from the 'second' drive which will not work and 
> the reason for the failure or whether it does load stage2 but stage2 
> looks in the wrong 'disk' for its config file.
> 
> So either way, it should also fail on a scsi system...

These seem to shift the first working drive into the first bios
drive as well as /dev/sda.  The same disk will boot whether I
put it in the 1st or 2nd (SCA hot-swap) slot. I have noticed
that some newer machines must be configured specifically for the
slot to use when booting and are even unhappy if you swap in
a different drive type in the same slot without reconfiguring
the bios boot selection so this may vary a lot among machines.

I did the grub setup by hand but have noticed that there are
different sets of instructions around that apply to IDE drives.
In any case, I think it is a good idea to keep a rescue CD
handy and understand how to re-install grub.

-- 
  Les Mikesell
   lesmikesell at gmail.com