[CentOS] Software RAID + LVM + Grub

Matthew Topper topperm9 at gmail.com
Mon Sep 20 08:51:58 EDT 2010


Thanks.  That third link especially helped.

On Sat, Sep 18, 2010 at 5:47 PM, Tom H <tomh0665 at gmail.com> wrote:
> On Sat, Sep 18, 2010 at 2:41 PM, Matthew Topper <topperm9 at gmail.com> wrote:
>> On Sat, 18 Sep 2010 17:42:59 +0200 Timo Schoeler <timo.schoeler at riscworks.net> wrote:
>>
>>> On 09/18/2010 05:13 PM, Matthew Topper wrote:
>>> > I'm playing with software RAID and LVM in some virtual machines and
>>> > I've run into an issue that I can't find a good answer to in the
>>> > docs.
>>> >
>>> > I have the following RAID setup:
>>> >
>>> > md0: sda1 and sdb1, RAID 1.  This is /boot
>>> >
>>> > md1: sda2 and sdb2, RAID 1.  This is a PV for LVM.
>>> >
>>> > VolGroup00, this is the volume group and md1 is the only PV in it.
>>> >
>>> > LogVol00 is swap
>>> > LogVol01 is /
>>> > LogVol02 is /home
>>> >
>>> > So, I tested to see what happens if I disable sdb in virtualbox.
>>> > Machine booted find and I was able to see that part of the raid
>>> > array was gone.
>>> >
>>> > I reattached the disk and rebuilt the array
>>> > mdam --add /dev/md0 /dev/sdb1
>>> > mdam --add /dev/md1 /dev/sdb2
>>> >
>>> > The array rebuilt without issue.  But now, if I remove sda, the
>>> > machine doesn't boot and grub complains.  The question I have is
>>> > how does one reinstall the boot sector at this point?  I'm a little
>>> > confused as far as to what device to install it on and what to
>>> > specify as the root.
>>> >
>>> > This is grub.conf if it helps:
>>> >
>>> > default=0
>>> > timeout=5
>>> > splashimage=(hd0,0)/grub/splash.xpm.gz
>>> > title CentOS (2.6.18-194.e15)
>>> >     root (hd0,0)
>>> >     kernel /vmlinuz-2.6.18-194.e15 ro
>>> > root=/dev/VolGroup00/LogVol01 initrd /initrd-2.6.18-194.e15.img
>>> >
>>> > Grub has always been a little confusing for me, so I guess I don't
>>> > understand.  What do the two root entries specify?  And again, my
>>> > main question is how do I reinstall grub to the repaired disk?
>>>
>>> http://wiki.centos.org/HowTos/CentOS5ConvertToRAID#head-fa2b73a28acdf965daa1e018962eaa8cbd94110c
>>
>> Entering those commands exactly worked, but I'm not sure why it
>> worked.  So, it's progress.
>>
>> I need to find some good reference on GRUB, which seems difficult
>> because most things I can find are about GRUB2, and CentOS has 0.97
>
> The commands installed grub into the mbr of sdb that way you can boot
> from either sda or sdb if the other is missing.
>
> You should always do that when booting from raid1
> http://wiki.centos.org/HowTos/SoftwareRAIDonCentOS5
>
> GRUB1 manual
> http://www.gnu.org/software/grub/manual/legacy/grub.html
>
> Good link (AFAIR)
> http://members.iinet.net.au/~herman546/p15.html
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