wiping an old LVM

Hi,
I have browsed the archives and not found a conclusive answer to this:
How much of an PV partition do I need to wipe with dd so that pvscan does not find it?

I have found that even if I wipe a partition table with dd and then repartition with the same sized partitions, the old PV and VG are still found. I tried zeroing the start of the LVM partition, but found this only worked consistently if I wiped nearly the entire partition. Where exactly is the metadata that needs to be zeroed?

I'd like to to wipe it regardless of any information about previous LVM configuration. This is for install scripts of cluster nodes which are re-imaged periodically. I'm using LVM 1.0.3.

Thanks,
Nathan

I have no idea if this is the way to do this officially but this worked for me.

I had three partitions slash, usr and var on lvm vgs made on three software raid devices.

I wanted to remove lvm 1 so I could try the 2.6 kernel - I guess I could have upgraded lvm but that seemed like more effort.

What I did was:

backup each partition. Then for each partition, make a new partition on a spare disk, mke2fs it, copy the data into it and change fstab to pick up the new location.

Reboot. The old vg is still picked up by vgscan and I could not get rid of them with lvremove/vgremove because it moaned that they were in use. However, then for each one in turn I did mke2fs on the filing system and then deleted /etc/lvmtab and rebooted. When the machine came up if then lost that pv,vg,lv.

Although I didn't try this, one thing I thought of was that you could delete /etc/lvmtab and edit the linuxrc script in /boot/initrd.img so that it didn't run vgchange -ay and so on on boot. You would then be able to get rid of stuff at your leisure without lvremove complaining stuff was in use.

Geoff Dolman
JDRF/WT Diabetes and Inflammation Laboratory
Cambridge Institute for Medical Research
University of Cambridge
http://www-gene.cimr.cam.ac.uk/todd/