Mailinglist Archive: opensuse (714 mails)

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Re: [opensuse] Double check: /boot on RAID 1
I think this implies that grub is installed on your RAID 1 (I assume
you are talking about a raid 1 /boot partition using the first
partition on each disk). This doesn't tell you anything about whether
grub has updated the MBR.

To install grub on both MBR's I would type (as root):

grub
grub> root (hd0,0)
grub> setup (hd0)
grub> root (hd1,0)
grub> setup (hd1)
grub> quit

I would be interested in what others have to say on this and whether
there is a way of specifying a "time out" so if the system can not
boot from hd0 it attempts to boot from hd1? (my guess is this would be
bios dependant)

On 30 September 2011 21:59, Michael Fischer <michael@xxxxxxxx> wrote:

Being one of the folks who tries to do the Subject,
I recently ran across an old thread on the list which confirmed
most of my experience with it, but mentioned that Yast (in the
installer mode) might not be putting grub, etc. on both disks'
MBR or /boot. After some web-digging, I tried the following:

grub> find /boot/grub/stage1
(hd0,0)
(hd1,0)

Can someone competent in the matter confirm for me that the above
does indeed mean that both disks in the array have had a working
grub written to both disks, and therefore, in the event of the
failure of one drive, the other is indeed bootable into a working system?

If not, why not and what should I do to "fix" the matter.

TIA.


Michael
--

I've used this setup for a long time on my RAID 1 array.

Michael, your syntax puts grub in the boot sector of the first partition on the
first and second boot disks. Philip's syntax puts grub in the MBR of those
disks. Note that if grub is being installed from the running OS (as opposed to
the grub shell with no OS running) it will use /boot/grub/device.map to
determine which of the disks correspond to hd0 and hd1, which may or may not be
the same as the bios boot device sequence. Assuming hd0 and hd1 are the bios
first and second boot devices, if booting from the first disk fails then the
bios will call the sector on the second disk. The array is immaterial to this
process.

YaST's boot manager module can be instructed to install grub to both the
partition boot sector and the master boot record. All YaST actually does is
write out the file /etc/grub.conf with syntax similar to the above and then
call grub in batch mode, the grub shell then does the actual install.

As an aside, a twist on the above is to install grub in the partition boot
sector, mark that partition active, and then install the "generic" boot code to
the MBR (so YaST uses grub to do the the former and the latter it does itself).
All the bios does in every case is hand-off to the strap code in the MBR of
the first active partition in the table. If grub is there, it has a pointer to
the /boot partition and using the file system locates the kernel. If the
generic code is in the MBR, that code calls the strap in the boot sector in the
first primary partition which is marked active (or "bootable").
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