[CentOS] preferred software RAID 10?

Ross S. W. Walker RWalker at medallion.com
Mon Jul 28 14:35:56 UTC 2008

Rudi Ahlers wrote:
> Ross S. W. Walker wrote:
> > 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.)
> >>
> >> (*) Anyway, you would boot from a Rescue CD or such and rename it ...
> >>     
> >
> > Yes, no problems, I had /boot mirrored across 4 drives (NAS box) and
> > grub installed on each.
> >
> > If you use labels for /boot in fstab you don't even need to edit fstab
> > from a rescue CD, just remove the failed first drive and boot.
> >
> Can you please explain this to me?
> I've never used labels before, so if you could maybe show me a sample of 
> how it's setup?

Disk labels are stored in file systems superblock.

For ext2/ext3 file systems you use the tune2fs and the -L option to define
a label, then you can refer to it in fstab like such:

LABEL=boot              /boot                   ext3    defaults        1 2

The problem with labels is, say you have an external USB drive and it
happens to have a label called 'boot' as well, well then it is
possible the OS will mount that instead (but grub will still use
the real 'boot' to boot off of as the physical disk is defined in
grub), then you will wonder why you still are booting the old
kernel after you have upgraded to the new one!


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