[Novalug] Asking early... maybe ok Fedora + HW RAID

[Peter Larsen]

On Wed, 2009-11-25 at 17:57 -0500, greg pryzby wrote:

> On 11/25/2009 04:36 PM, Peter Larsen wrote:
> > On Wed, 2009-11-25 at 15:56 -0500, greg pryzby wrote:
> >> I received a box w/ hardware RAID with Fedora 11. It worked great. I
> >> tried to preupgrade and on reboot I got a mismatched size error. So I
> >> googled to see what could be going on w/o much info. There was an
> >> preupgrade in updates-testing that was recommended so I tried that, same
> >> issue. From looking at OS level, RAID looked ok.
> >
> > What kind of "hardware" raid? The hardware raid my box came with turned
> > out to be software and a lot worse that our md drivers. The problem you
> > need to be aware of isn't whether the kernel supports it, but if grub
> > supports it. Grub2 is supposed to have better support, but it's a lousy
> > documented project (it's included with Fedora - good luck is all I can
> > say). I had a simple RAID0 (stripe) and grub failed miserably
> > reading/understanding the raid on the system board.
> >
> > If you're going RAID1 you may be more lucky since it shouldn't matter
> > what disk it chooses - unless there's truely a Hw raid signature on the
> > disk that'll confuse grub.
> 
> 3ware 9650SE and it is supported in Linux, in the kernel. the crappy mb 
> raid isn't being used. pci-e card


But is it supported by GRUB? What does Grub after phase 1 has loaded
from MBR+boot?  


> I built RAID 5 via the firmware
> 
> However, looking at dmesg, they talk about RAID 6, ok whatever. 
> shouldn't matter from a quick search.


THAT should not matter if it's true hardware raid. The actual raid
mechanisms are hidden from the OS/boot loader.


> There are 2 partitions (is that the right term?). it asked in firmware 
> about boot size and it created 2 partitions.


Sure could be. Same rules applies as a single disk. You need a boot
partition. And something for the rest. Grub2 allows you to place the
boot on LVM2 - so you don't need any partitions then. Can't wait!

But your HW raid should NOT care at all about "partitions". If you're
doing RAID 6 you have at least 4 disks of the same size and dimension.
Your HW Raid should simply make a single disk-image (logical) out of the
4 disks and present this volume to the OS. The OS will then do what it
usually does, with partitions and all (including MBR). In some cases,
metadata about the RAID is stored on disks - but I wouldn't expect to
see that in partitions. That should be hidden from you.


> I think that maybe where things are wacky or maybe there is ONLY 
> hardware raid5 disks.


The actual raid level should not matter if it's true hardware. What
happened to my software card (I checked your card, it has a processor on
it so it should be true hardware) was that once grub-stage 1 was over,
it couldn't find the partition and it's data to boot from.


-- 

Best Regards
  Peter Larsen

Wise words of the day:
No, that's wrong too.  Now there's a race condition between the rm and
the mv.  Hmm, I need more coffee.
	-- Guy Maor on Debian Bug#25228
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