[linux-lvm] SUMMARY: Help! All PVs present but vgscan fails to assemble volume group

[Lars Kellogg-Stedman]

Everything is working once again, and I wanted to summarize my 
experience to the list in the hopes that someone else will find it helpful.

There appear to have been two problems at work here:

(1) The list compacting code in pv_read_all_pv_of_vg() is buggy, and in 
common situations would lose track of some PVs.  I submitted a very 
simple patch for this to Heinz earlier today, but I've since put a 
cleaner version up at <http://larsshack.freeservers.com/lvm/>.

(2) It looks as if the 'vgmerge' command may have trodded upon on-disk 
information on /dev/md0, erasing both the LV table and the mappings for 
the first 173 PEs.

Andreas provided the information I needed to manually reconstruct the 
data lost due to (2).  In fact, Andreas has been extraordinarily helpful 
in tracking down both the cause and a solution to this problem, and I'd 
like to thank him here for his time and effort.

I have not yet investigated the vgmerge problem in any detail, so I 
don't know why it corrupted the on-disk data.

-- Lars