On 2004 09 10 (Friday) 09:14, Alexandre Oliva wrote:
> On Sep 10, 2004, Yusuf Goolamabbas <yusufg@xxxxxxxxxxxx> wrote:
>
> > Hi, I haven't tested FC3test as yet and wanted to ask if grub in FC3
> > would do the right thing when installing on a software raid-1 boot array
> > (ie, that it would write to the MBR on both disks) so if there was a
> > disk failure, the machine would still come up.
>
> The right thing depends on your BIOS and on the disk failure mode.
>
> Consider, for example, that you have two disks, 0x80 and 0x81. If you
> naively install boot information on both disks' boot records such that
> it looks for the boot partition in the disk itself, if you remove disk
> 0x80, disk 0x81 may not boot because it becomes 0x80. OTOH, if you
> replace disk 0x80, the BIOS will likely try to boot from it, and
> fail. If it fails over to the other disk, or if you change the BIOS
> settings so as to boot from this other disk, then it might be
> renumbered to 0x80, or it might not. You can't have it work both
> ways, unfortunately.
>
> Then consider more interesting scenarios like multiple disks and you
> may realize that, when lilo claims to be safe for raid 1, it's only
> for a some failure scenarios, and within certain BIOS behaviors.
>
> > I don't know if Grub is capable of this task
>
> It is, but you have to do it yourself, implying what kind of failure
> scenarios you're trying to prepare for.
>
I have a Pentium 4 3000E and EPox EP-4PCAI with three Seagate
ST3160023A disks. I'm testing it with software raid1 and raid5 to
see how it works. I use (waiting for additional IDE controller):
--- cut ---
# grub
grub> root (hd0,0)
grub> setup (hd0)
grub> device (hd0) /dev/hdb
grub> root (hd0,0)
grub> setup (hd0)
grub> device (hd0) /dev/hdc
grub> root (hd0,0)
grub> setup (hd0)
--- cut ---
When I remove any of the disks (or swap them randomly) it boots
without problems (even changing hdc to hdd). My setup is:
--- cut ---
# cat /proc/mdstat
Personalities : [raid1] [raid5]
md1 : active raid5 hda2[0] hdb2[1] hdc2[2]
312046080 blocks level 5, 256k chunk, algorithm 2 [3/3] [UUU]
md0 : active raid1 hda1[0] hdb1[1] hdc1[2]
264960 blocks [3/3] [UUU]
-- cut ---
md0 is /boot and everything else is on md1 (LVM). I don't know if
BIOS moves the first available disk to 0x80, but GRUB loads from any
disk (even if I connect hdc only). I'll try this with more machines
when I have time to.
--
Regards,
Doncho N. Gunchev Registered Linux User #291323 at counter.li.org
GPG-Key-ID: 1024D/DA454F79 http://pgp.mit.edu
Key fingerprint = 684F 688B C508 C609 0371 5E0F A089 CB15 DA45 4F79
