software raid

[C M Reinehr]

Vu,

On Thu 07 August 2008 20:24, Vu Pham wrote:
> Vu Pham wrote:
> [...]
>
> > My RHEL server, using GRUB, has /boot on raid-1. Disk Druid told me if I
> > set up /boot on RAID, then only RAID-1 can be used.
> >
> >
> > Grub config shows
> >         root (hd0,0)
> >         kernel /vmlinuz-2.6.18-53.el5PAE ro root=/dev/md2 rhgb quiet
> >         initrd /initrd-2.6.18-53.el5PAE.img
> >
> > so I think the boot-loader, at boot time, just loads the kernel as if it
> > is in a normal ext3 partition
>
> To test that theory, I removed the first hard drive of the software
> raid-1 that has /boot. The system was still  working fine at that moment
> and mdadm did report that problem. But when I rebooted the system, the
> whole system just crashed right at GRUB.
>
>  From that test, I think that for sfotware-raid-1 /boot partition,  raid
> works only after the kernel is loaded ( and the raid driver is loaded ).
> At boot time, just the first disk of that raid-1 to be used as a
> non-raid disk because no raid driver exists at that moment.
>
> Vu

You can overcome this problem by installing GRUB to the MBR of the second 
drive in the raid 1 array, as well as to the first drive. You can use 
grub_install, etc. or you can just dd the mbr from the first drive to the 
second drive. This way, if the first drive is inoperable you still can boot 
from the second drive (which is, after all, just a mirror image of the first 
drive).

cmr

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