[CentOS] Moving LVM from one machine to another

[Robert Heller]

At Sat, 9 Jan 2010 08:17:11 -0500 CentOS mailing list <centos at centos.org> wrote:

> 
> On Fri, Jan 08, 2010 at 11:02:12PM -0500, Robert Heller wrote:
> > At Fri, 8 Jan 2010 22:40:21 -0500 CentOS mailing list <centos at centos.org> wrote:
> > > Now I've moved those 5 disks onto a CentOS5 machine and the RAID array
> > > is being rebuilt.  However the LVM structures weren't detected at boot
> > > time.  I was able to "vgscan" and 'vgchange -a y' to bring the volume
> > > online and then fsck the logical volumes.
> > > 
> > > But I was concerned this didn't happen at boot time.  Do I need to do
> > > anything else, or have the commands I've run done sufficient?
> > > 
> > > FWIW, this machine has no other LVM (nor RAID) disks on it.
> > 
> > This is why.  Unless the machine 'knows' to look for LVM (eg has the
> > mumble mumble in /etc/lvm/), it wouldn't look for it during start up.  And
> > unless it's root file system is on LVM its initrd won't have the
> > "vgscan" and 'vgchange -a y' commands in the init script.
> 
> So what's the fix?  How do I get the right "mumble mumble"? :-)

You do a "vgscan" and 'vgchange -a y' manually.  This should put the
right stuff in /etc/lvm/.

It is rare/unusual to 'add' LVM volumns to a running system from some
'outside' source (as you did via a disk transplant).  Linux installers
will do the "vgscan" and 'vgchange -a y' during the install process and
vgcreate updates /etc/lvm/, so the problem rarely comes up.

> 
> Thanks!
> 
> > > (only 5 more hours for the rebuild to complete!)
> > > 
> > 
> > And hopefully, you won't get a disk error in the those errors and lose
> > the whole array.
> 
>    % cat /proc/mdstat
>    Personalities : [raid6] [raid5] [raid4] 
>    md3 : active raid5 sdf1[4] sde4[3] sdd3[2] sdc2[1] sdb1[0]
>          3907039744 blocks level 5, 64k chunk, algorithm 2 [5/5] [UUUUU]
>       
>    unused devices: <none>
> 
> No problem :-)
> 

-- 
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