[gentoo-amd64] Quick grub question

[gentoo-amd64] Quick grub question

[Richard Freeman]

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Ok, I am trying to get my raid working.  I have /dev/hda,b,c,d and
/dev/sda,b,c.  My boot partition is on /dev/sda1 and /dev/sdb1
(mirrored).  So, how do I set that up?

Grub gives me:

grub> find /boot/grub/stage1
 (hd0,0)
 (hd3,0)
 (hd4,0)

You can ignore hd0,0 - that is my old non-raid boot partition - it will
get blown away once I'm migrated to the raid.

I'm not sure if the drive numbers that grub sees will change when I boot
off of sda or sdb.  I did try to set things up following the various
howtos and it didn't work, but they all tend to assume your boot drive
is hd0.

Any pointers?  And don't ask why I have so many drives and am only now
starting to set up a RAID...  :)  Suffice it to say my current lvm
config makes me nervous...
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[gentoo-amd64] Re: Quick grub question

[Duncan]

Richard Freeman <rich@thefreemanclan.net> posted
463D15D0.1030105@thefreemanclan.net, excerpted below, on  Sat, 05 May 2007
19:40:00 -0400:

> Ok, I am trying to get my raid working.  I have /dev/hda,b,c,d and
> /dev/sda,b,c.  My boot partition is on /dev/sda1 and /dev/sdb1
> (mirrored).
>  So, how do I set that up?
> 
> Grub gives me:
> 
> grub> find /boot/grub/stage1
>  (hd0,0)
>  (hd3,0)
>  (hd4,0)
> 
> You can ignore hd0,0 - that is my old non-raid boot partition - it will
> get blown away once I'm migrated to the raid.
> 
> I'm not sure if the drive numbers that grub sees will change when I boot
> off of sda or sdb.  I did try to set things up following the various
> howtos and it didn't work, but they all tend to assume your boot drive
> is hd0.
> 
> Any pointers?  And don't ask why I have so many drives and am only now
> starting to set up a RAID...  :)  Suffice it to say my current lvm
> config makes me nervous...

Sounds like you /should/ be nervous. =8^(

OK, I'm tired and I'm not sure I'm answering the question you are asking 
as I'm not sure I'm correctly parsing it, but let's see if this helps.

Think of it this way, when each drive is configured in BIOS to boot, 
it'll probably see itself as hd0, with the BIOS switching around the 
others accordingly to make it that way.

Rather than try to figure out which drive was which and get grub 
installed correctly in them all (I have four in my RAID) from my running 
system, I installed grub to a floppy, and booted that, so all the hard 
drives appeared in their "natural" BIOS order.  Then one by one, I 
installed to them from the floppy, then when I was done, I tested by 
pointing the BIOS at each one to boot from, and then doing the same 
thing, but with the other drives removed, to be sure it could find grub 
and grub could find /boot on the single remaining drive of the mirror set 
with or without all the others in the mirror set there.

As noted above, with the BIOS pointed at a drive to boot, it may see 
itself as hd0, regardless of where it's normally located.  You can test 
this, by configuring root (hd0,0) for each install, then point the BIOS 
at it and see if it find /boot.  If it does, you know that's what the 
BIOS is doing, reassigning each drive as the first one.  If it doesn't, 
you know that it's not, and you probably need to use root (hd3,0) when 
installing grub.  Once grub is installed, however, you may be able to 
boot it and figure out where it needs to point, if it's not pointed at 
the right place.

Hope that helps, and didn't leave you even more confused.  I know I did 
it, but I took it a step at a time, and as I said, installed grub to a 
floppy and booted it to figure out what was going on, then installed to 
the hard drive from the floppy.

-- 
Duncan - List replies preferred.   No HTML msgs.
"Every nonfree program has a lord, a master --
and if you use the program, he is your master."  Richard Stallman

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Re: [gentoo-amd64] Quick grub question

[Florian D.]

hello,
the drive ordering thing is explained by Duncan already. I just want to point out that if you want
to have your root partition on the raid too and if you are using the new superblock version(>=1),
you should be aware of the fact, that it is not possible to auto-assemble the array during the boot
process. Neither the normal raid-autodetect nor a kernel command line like
raid=noautodetect root=/dev/md1 md=1,/dev/sda2,/dev/sdb2,/dev/sdc2
will work. In this case, you have to use an initramfs to assemble your root-raid, or just use the
old 0.90 superblocks, which is the default, I think.
I just wanted to tell you that, because I had exactly the same issue and setting up the initramfs
was quite a lot of work (and IMHO only poor documentation available).

cheers, f
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Re: [gentoo-amd64] Quick grub question

[Richard Freeman]

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Florian D. wrote:
> hello,
> the drive ordering thing is explained by Duncan already. I just want to point out that if you want
> to have your root partition on the raid too and if you are using the new superblock version(>=1),
> you should be aware of the fact, that it is not possible to auto-assemble the array during the boot
> process. Neither the normal raid-autodetect nor a kernel command line like
> raid=noautodetect root=/dev/md1 md=1,/dev/sda2,/dev/sdb2,/dev/sdc2
> will work. In this case, you have to use an initramfs to assemble your root-raid, or just use the
> old 0.90 superblocks, which is the default, I think.
> I just wanted to tell you that, because I had exactly the same issue and setting up the initramfs
> was quite a lot of work (and IMHO only poor documentation available).
> 

Thanks to both of you.  I'll, experiment with that the next time I have
some downtime.  I have version 00.90.03 superblocks at the moment so it
sounds like I should be OK.

I noticed the new grub-2 is supposed to take care of a lot of this mess,
or at least it looks like it.  It would be a lot nicer to just say "root
(md1)" and be done with it!

Hopefully by the time the new superblocks become standard somebody will
update the various HOWTOs to explain how to set up the initrd to make it
work...
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Re: [gentoo-amd64] Quick grub question

[Joshua Hoblitt]

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On Sun, May 06, 2007 at 07:05:30PM -0400, Richard Freeman wrote:
> I noticed the new grub-2 is supposed to take care of a lot of this mess,
> or at least it looks like it.  It would be a lot nicer to just say "root
> (md1)" and be done with it!

grub2 is also pretty poorly documented and seems to be stagnating - I
would be surprised if they got a stable release out the door in the next
year.  The devs have refused to patch grub 0.9.x to support GPT
partitions, not on a technical basis but because it's a "grub2 feature".
Mean while the world has moved on and having a boot block device > 2TB
isn't that usual anymore.  I have to build my own liveCDs with a patched
grub because of this.

-J

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