Re: Use LVM on /dev/mapper/diskname and iSCSI

["S. J. van Harmelen" <svh@dds.nl>]

P.S. pvs only scanned the real disks and not the /dev/mapper/diskname
disks. So some of the scan's where rejected because the path to that
path was the redudant path.

But I assume that the /dev/mapper/diskname will have the exact same lvm
info written on it, ass it is in fact the real disk (/dev/sdi for
example)?

Sander


On Mon, 2007-11-19 at 15:06 +0100, Tore Anderson wrote:
> * S. J. van Harmelen
> 
> > I have a couple of LUN's that are handled by the multipath driver.
> > This works great, but now I want to use LVM so I can take snapshots
> > of one LUN to another LUN.
> > 
> > Can someone tell me how to do this?
> > 
> > When I do pvcreate /dev/mapper/diskname I get an error that the disk
> > is already part of an volume group. But I sertainly did not configure
> > that.
> > 
> > Can it be that the multipath driver of devmapper did that?
> 
> If you have a PV signature on the volume, LVM might have used one of the
> paths instead of using the multipath'ed device under /dev/mapper.  You
> should be able to check this by running the command "pvs" - it should
> list all the detected PVs on your system.
> 
> If this was the problem, you can avoid it by instructing LVM to not scan
> SCSI devices directly, by adding a line in /etc/lvm/lvm.conf like this:
> 
> device {
>   filter = [ "a|^/dev/mapper/.*|", "r|.*|" ]
> }
> 
> This will make LVM only look at devices in /dev/mapper/ as possible PV
> candidates, ignoring all other devices.  Beware if you have a PV on the
> internal drives though, you might want to have something like this
> instead in that case (if that PV is on /dev/sda2, for instance):
> 
>   filter = [ "a|^/dev/mapper/.*|", "a|^/dev/sda2$|", "r|.*|" ]
> 
> Make sure lvm.conf makes its way into the initramfs if you start the LVM
> stuff there.  I know Ubuntu doesn't include this file by default, at least.
> 
> Regards