[CentOS] preferred software RAID 10?

David Mackintosh David.Mackintosh at xdroop.com
Fri Jul 18 01:15:12 UTC 2008


On Fri, Jul 18, 2008 at 12:31:19AM +0200, Kai Schaetzl wrote:
> Rudi Ahlers wrote on Thu, 17 Jul 2008 23:10:48 +0200:
> 
> > > /boot shouldn't be mirrored, as the BIOS won't know how to boot it. 
> > > leave /dev/sdb1 the same size as /dev/sda1 and call it /boot2 and try 
> > > to remember to copy /boot to /boot2 each time you update the kernel.
> > I understand this, but how do you boot from /boot2 on the second HDD if 
> > the 1st have failed?
> 
> You don't (*). I don't understand John's advice here. There is no problem 
> md mirroring /boot. You just need to install grub a second time on the 
> other disk. For that you have to boot from it. (I think I also did it 
> successfully without booting from the other disk in the past, but last 
> time I tried it it didn't want to work like I remembered it should.)

I think you mean "if you want to boot from it, you have to install
grub on it".  I've done this.  It means if the first disk fails, you
can then physically remove the failed disk, put the survivor in as
the first disk, then boot from that.

To install grub to the second disk:

# grub
> device (hd0) /dev/sdb
> root (hd0,0)
> setup (hd0)
(blah blah blah)
Running "install /boot/grub/stage1 (hd0) (hd0)1+16 p (hd0,0)/boot/grub/stage2
/boot/grub/grub.conf"… succeeded
Done.
> quit

(or /dev/hdb, or whatever is appropriate).

To get back to the OP: I've done a RAID-10 under CentOS, and the
problem I encountered was that the kernel wasn't smart enough to
assemble the RAID without a properly populated /etc/mdadm.conf file.

See the details at http://wiki.xdroop.com/space/Linux/Software+Raid+compound+devices

-- 
 /\oo/\
/ /()\ \ David Mackintosh | 
         dave at xdroop.com  | http://www.xdroop.com
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