[rhelv6-list] LVM over dm-multipath

[Greg_Swift at aotx.uscourts.gov]

rhelv6-list-bounces at redhat.com wrote on 03/25/2011 08:19:44 AM:

> After playing with RHEL6 in VM's for a few weeks we finally decided to
> upgrade one of our existing production systems to RHEL6.  It's an older
> system, and relatively non-critical, so we had some downtime with it.
> The system is connected to an iSCSI SAN via Qlogic iSCSI HBA's, but we
> disconnected those during the install.  We installed RHEL6 and
> everything seemed fine so we reconnected the SAN, performed the
> multipath config, ran vgscan and the existing LVM volumes were found and
> everything seemed great.
>
> However, the problems came up when we rebooted.  The system mounted
> everything just fine, including the SAN volumes, however, we noticed
> that LVM is connecting directly to first physical disk rather than to
> the multipath target.  If we deactivate the LVM and reactive it after
> the system boots, then the LVM will be accessed via the multipath
> device.  It appears that the RHEL6 boot process is activating LVM prior
> to activating multipath.
>
> We've tried several options, and found a reference to what sounded like
> the problem in the RHEL6 technical notes which told us to create a new
> udev rule, but that didn't seem to change anything.
>
> Has anyone else seen this or is this something strange only in our
> environment?  Are we doing something obviously wrong?  Any options on
> where to look?

You might try uncommenting this line in /etc/lvm/lvm.conf (adjusting for
local matches as necessary):

# preferred_names = [ "^/dev/mpath/", "^/dev/mapper/mpath", "^/dev/[hs]d" ]

-greg