One of my machines has an lvm2 volume group spread across three disks. One died - here's how I rescued some of the data
Very luckily - the dead disk contained one whole logical volume - used for media storage. This meant that all the other logical volumes were there - but - lvm wouldn't start.
If I'd found out about it in time then this should have been enough:
vgreduce --removemissing vg0
However - by the time I found that the system was in a worse state (wouldn't boot even to single user mode).
So - here's how I got the data off using knoppix.
Boot to knoppix then switch to a tty.
The device mapper module is present - but not lvm - let's sort that out
modprobe dm_mod apt-get update apt-get install lvm2
Now we can start using it. Let's get the tool symlinks in place
cd /sbin ln -s lvmiopversion vgscan ln -s lvmoipversion vgchange
Now we can look at the data
vgscan vgchange -a y cd /mnt mkdir home mount -t xfs /dev/mapper/vg0-home home
Notes - I've got xfs logical volumes. All the volumes that were not on the dead disk are mountable. I had already run the vgreduce command before this point.
My thanks to Klaus Pieper and the debian-users mailing list for this one :) A life saver.