[WBEL-users] multiple md devices & lvm

[Kirby C. Bohling]

On Tue, Feb 08, 2005 at 08:59:17AM -0500, Toby Bluhm wrote:
> Has anyone tried using lvm on a box that has more than one md device with one device being raid5?

I've done that.

[root at vulture root]# cat /proc/mdstat
Personalities : [raid1] [raid5]
read_ahead 1024 sectors
Event: 5
md4 : active raid5 hda1[0] hdb1[1] hdc1[2] hdd1[3]
      878907648 blocks level 5, 256k chunk, algorithm 0 [4/4] [UUUU]

md1 : active raid1 sdb1[1] sda1[0]
      208704 blocks [2/2] [UU]

[root at vulture root]# cat /etc/issue
White Box Enterprise Linux release 3.0 (Liberation Respin 1)
Kernel \r on an \m

[root at vulture root]# uname -a
Linux vulture.birddog.com 2.4.21-15.0.2.ELsmp #1 SMP Fri Jun 18 23:13:20 EDT 2004 i686 i686 i386 GNU/Linux

(It's a little behind on the kernel, but everything on the system is
LVM except for /, /boot and swap).

> 
> The box has / & /boot on mirrored md. I can create many more
> striped or mirrored devices with the other disks & add them to
> lvm, create a vg, create a lv, create ext3 fs and it all works
> fine. However, if I make a raid5, add it to lvm, etc it all works
> fine until I reboot - system complains it can't find ext2
> superblocks on the lv.  If I just put the fs right on the md, that
> works fine too. Just seems that when lvm is involved, it goes down
> the toilet.

My guess is that you need to rebuild your initrd w/ the raid5 (and
the xor) modules.  You'll need the RAID5 added early on so the LVM
can autodetect in with vgscan/vgchange while running
/etc/rc.d/rc.sysinit if I remember correctly.

I ran into this on several machines where I added RAID5 after the
initial install.

There are three ways to do this:

1.  Do it by hand by munging the initrd by mounting it loopback.

2.  Just uninstall the kernel, and then reinstall the kernel.
(Alternatively, install an older kernel, reboot onto it, then
uninstall the current kernel, then reinstall it, then reboot to the
newer kernel).  That should fix the problem.

3.  Run mkinitrd by hand with the proper options.

> 
> I have other wb3 boxes using lvm and a raid5 as the only md device
> with no problems.  I ran into this before, on a rh9 box, but I
> thought it was due to me trying & tweaking to get xfs & other
> stuff working using a stock kernel., non-standard rpms, etc.

Let me guess you added the RAID5 after you did the initial install.
Gets me every time.

> 
> Is this an lvm thing or a RedHat thing?
> 
> Thanks
> 
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