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Re: Will FC3 grub DTRT wrt installation on software RAID-1 boot arrays

On Sep 10, 2004, Yusuf Goolamabbas <yusufg outblaze com> 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.

Alexandre Oliva             http://www.ic.unicamp.br/~oliva/
Red Hat Compiler Engineer   aoliva {redhat com, gcc.gnu.org}
Free Software Evangelist  oliva {lsd ic unicamp br, gnu.org}

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