[olug] lvextend

Christopher Cashell topher-olug at zyp.org
Wed Oct 20 15:05:00 UTC 2010

On Wed, Oct 20, 2010 at 8:16 AM, Noel Leistad - METC <noel at metc.net> wrote:
> SAN connected to 2-node cluster
> tried to extend an lvm volume on a SAN which supposedly succeeded.
> node1 sfdisk shows extended size, when mounted: df shows old_size
> node2 sfdisk shows old_size, when mounted: df shows old_size
> have umounted/remounted on each node, results remain same.

Be careful when using LVM in a clustered environment.  LVM is *not*
cluster aware, and you can get yourself out of sync and in an ugly
place if you aren't careful.  Basically, when making LVM changes, you
want to make sure that no other boxes in the cluster are using the LVM
volumes in any way.  That's the only safe way to make changes.

I would suggest using lvchange and then vgchange to set the volumes
and volume groups as unavailable to the cluster nodes where you aren't
making the changes, while you're making the changes.  After you make
changes (or, if you've already made changes), try running 'pvscan',
'vgscan', and 'lvscan' (in that order) on all of the cluster nodes to
try to re-read the available meta-information for the volumes.  If you
changed the LUN size underneath LVM, you'll have to rescan the SCSI
(fibre) bus or reboot the box to pickup those changes.

Also, you may want to look into clvm.  It's a Cluster-Aware extension
to LVM from Red Hat, included with RHEL/CentOS (may require cluster
suite for RHEL), and also available on Debian and Ubuntu.  It provides
a small daemon (clvmd) that propagates LVM changes to all the cluster
nodes, making LVM safer and easier to use in a cluster setup.

> #  Noel Leistad                                       #


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